全文获取类型
收费全文 | 60620篇 |
免费 | 2302篇 |
国内免费 | 3887篇 |
专业分类
测绘学 | 2604篇 |
大气科学 | 5477篇 |
地球物理 | 11559篇 |
地质学 | 27126篇 |
海洋学 | 5198篇 |
天文学 | 8293篇 |
综合类 | 3036篇 |
自然地理 | 3516篇 |
出版年
2023年 | 249篇 |
2022年 | 899篇 |
2021年 | 1232篇 |
2020年 | 1119篇 |
2019年 | 1229篇 |
2018年 | 6432篇 |
2017年 | 5571篇 |
2016年 | 4177篇 |
2015年 | 1292篇 |
2014年 | 1684篇 |
2013年 | 2202篇 |
2012年 | 2721篇 |
2011年 | 4670篇 |
2010年 | 3828篇 |
2009年 | 4273篇 |
2008年 | 3625篇 |
2007年 | 4247篇 |
2006年 | 1789篇 |
2005年 | 1145篇 |
2004年 | 1259篇 |
2003年 | 1316篇 |
2002年 | 1258篇 |
2001年 | 977篇 |
2000年 | 777篇 |
1999年 | 703篇 |
1998年 | 615篇 |
1997年 | 622篇 |
1996年 | 502篇 |
1995年 | 508篇 |
1994年 | 458篇 |
1993年 | 358篇 |
1992年 | 362篇 |
1991年 | 283篇 |
1990年 | 278篇 |
1989年 | 286篇 |
1988年 | 231篇 |
1987年 | 240篇 |
1986年 | 224篇 |
1985年 | 241篇 |
1984年 | 235篇 |
1983年 | 229篇 |
1982年 | 224篇 |
1981年 | 211篇 |
1980年 | 200篇 |
1979年 | 203篇 |
1978年 | 171篇 |
1977年 | 155篇 |
1976年 | 152篇 |
1975年 | 157篇 |
1973年 | 179篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Detailed data obtained on surface oil samples from the Bazhenovskaya Formation in the latitudinal segment of the Ob River
area indicate that the composition of the oil is largely controlled by the P-T conditions in the reservoir. It was determined that the generation of hydrocarbon fluids starts at higher temperatures (T
f > 100°C) if the fluid reflux is hindered and the formation pressures are anomalously high. In systems with the free reflux
of hydrocarbon fluids, the processes generating oil and gas are different. The composition of oil in the Bazhenovskaya Formation
with the free reflux of hydrocarbon fluids is largely controlled by migration processes, which determine, along with the P-T parameters, the physicochemical characteristics of the oils and their concentrations of hydrocarbon groups and individual
hydrocarbons.
Original Russian Text ? O.F. Stasova, A.I. Larichev, N.I. Larichkina, 2006, published in Geokhimiya, 2006, No. 9, pp. 996–1005. 相似文献
992.
993.
I. N. Tomson O. P. Polyakova V. Yu. Alekseev V. A. Baskina 《Geology of Ore Deposits》2006,48(1):74-76
Two types of metalliferous carbonaceous rocks that differ in associated metals are considered. One of them is characterized by gold occurring in finely dispersed arsenopyrite and arsenic-bearing pyrite, and the other, by finely impregnated native metals in carbonaceous matter. Rocks of the first type also contain elements of the platinum group, while those of the second type bear rhenium, silver, iron, molybdenum, and other metals. Graphitic mineralization is usually localized in the shear zone associated with alkaline basalts. 相似文献
994.
995.
The Tyrell catchment lies on the western margin of the Riverine Province in the south-central Murray Basin, one of Australia’s most important groundwater resources. Groundwater from the shallow, unconfined Pliocene Sands aquifer and the underlying Renmark Group aquifer is saline (total dissolved solids up to 150,000 mg/L) and is Na-Cl-Mg type. There is no systematic change in salinity along hydraulic gradients implying that the aquifers are hydraulically connected and mixing during vertical flow is important. Stable isotopes (18O+2H) and Cl/Br ratios indicate that groundwater is entirely of meteoric origin and salts in this system have largely been derived by evapotranspiration of rainfall with only minor halite dissolution, rock weathering (mainly feldspar dissolution), and ion exchange between Na and Mg on clays. Similarity in chemistry of all groundwater in the catchment implies relative consistency in processes over time, independent of any climatic variation. Groundwater in both the Pliocene Sands and Renmark Group aquifers yield ages of up to 25 ka. The Tyrrell Catchment is arid to semi-arid and has low topography. This has resulted in relatively low recharge rates and hydraulic gradients that have resulted in long groundwater residence times. 相似文献
996.
Yu. V. Plotkina E. B. Sal’nikova A. B. Kotov M. D. Tolkachev M. R. Pavlov 《Petrology》2006,14(2):201-208
The paper reports results obtained by the complex studying of zircon crystals from rocks of various genesis. Zircon is one of the minerals most often used as geochronometers. It also provides genetic information on superimposed processes that is “recorded” in the external and internal morphology of its crystals. This mineral is thoroughly examined to select its unaltered crystals for U-Pb dating by the single-grain method. Zircon grains are selected with the use of optical and electron microscopy and cathodoluminescence. This publication presents the first results obtained by examining zircon by computer microtomography (μCT) and the results of the studying of the external and internal structure by conventional techniques ([optical microscopy and SEM (SE and CL)]. The paper demonstrates the advantages of the application of the μCT techniques to the selection of targets for U-Pb zircon dating: there is no need for the special preparation of the samples and no material is destructed. However, this technique may be not informative enough if the zircon contains inherited core whose density does not differ from the density of the surrounding mineral. 相似文献
997.
998.
Aierken Sidike X.-M. Wang Alifu Sawuti H.-J. Zhu I. Kusachi N. Yamashita 《Physics and Chemistry of Minerals》2006,33(8-9):559-566
Natural calcite from Kuerle, Xinjiang, China, shows orange-red fluorescence when exposed to short-wave ultraviolet (UV) light (Hg 253.7 nm). Photoluminescence (PL) emission and excitation spectra of the calcite are observed at room temperature in detail. The PL emission spectrum under 208 nm excitation consists of three bands: two UV bands at 325 and 355 nm and an orange-red band at 620 nm. The three bands are ascribed to Pb2+, Ce3+ and Mn2+, respectively, as activators. The Pb2+ excitation band is observed at 243 nm, and the Ce3+ excitation band at 295 nm. The Pb2+ excitation band is also observed by monitoring the Ce3+ fluorescence, and the Pb2+ and Ce3+ excitation bands, in addition to six Mn2+ excitation bands, are also observed by monitoring the Mn2+ fluorescence. These indicate that four types of the energy transfer can occur in calcite through the following processes: (1) Pb2+ → Ce3+, (2) Pb2+ → Mn2+, (3) Ce3+ → Mn2+ and (4) Pb2+ → Ce3+ → Mn2+. 相似文献
999.
The integrated radio luminosities of 311 long-period (P > 0.1 s) and 27 short-period (P < 0.1 s) pulsars have been calculated using a new compilation of radio spectra. The luminosities are in the range 1027 ? 1030 erg/s for 88% of the long-period pulsars and 1028 ? 1031 erg/s for 88% of the short-period pulsars. We find a high correlation between the luminosity L and the estimate L 1 = S 400 d 2 from the catalog of Taylor et al. The factor η for the transformation of the rotational energy of the neutron star into radio emission increases-decreases with increasing period for long-period and short-period pulsars. The mean value of η is ?3.73 for the long-period and ?4.85 for short-period pulsars. No dependence was found between L and the pulsar’s kinematic age t k = |z|/〈v z〉, where |z| and 〈v z〉 = 300 km/s are the pulsars’ height above the plane of the Galaxy and mean velocity. A dependence of L on the rate of rotational energy losses ? was found for both groups of pulsars. It is shown that L ∝ ? 1/3 for the entire sample. The pulsar luminosity function is constructed, and the total number and birth rate of pulsars in the Galaxy are calculated. 相似文献
1000.