全文获取类型
收费全文 | 22204篇 |
免费 | 4990篇 |
国内免费 | 7078篇 |
专业分类
测绘学 | 2667篇 |
大气科学 | 4205篇 |
地球物理 | 4776篇 |
地质学 | 12746篇 |
海洋学 | 4293篇 |
天文学 | 778篇 |
综合类 | 2085篇 |
自然地理 | 2722篇 |
出版年
2024年 | 118篇 |
2023年 | 416篇 |
2022年 | 1120篇 |
2021年 | 1354篇 |
2020年 | 1154篇 |
2019年 | 1387篇 |
2018年 | 1343篇 |
2017年 | 1211篇 |
2016年 | 1353篇 |
2015年 | 1382篇 |
2014年 | 1458篇 |
2013年 | 1650篇 |
2012年 | 1728篇 |
2011年 | 1713篇 |
2010年 | 1778篇 |
2009年 | 1583篇 |
2008年 | 1608篇 |
2007年 | 1515篇 |
2006年 | 1280篇 |
2005年 | 1118篇 |
2004年 | 850篇 |
2003年 | 634篇 |
2002年 | 646篇 |
2001年 | 692篇 |
2000年 | 643篇 |
1999年 | 689篇 |
1998年 | 524篇 |
1997年 | 462篇 |
1996年 | 471篇 |
1995年 | 395篇 |
1994年 | 323篇 |
1993年 | 312篇 |
1992年 | 265篇 |
1991年 | 207篇 |
1990年 | 164篇 |
1989年 | 131篇 |
1988年 | 133篇 |
1987年 | 77篇 |
1986年 | 64篇 |
1985年 | 49篇 |
1984年 | 32篇 |
1983年 | 27篇 |
1982年 | 39篇 |
1981年 | 33篇 |
1980年 | 21篇 |
1979年 | 22篇 |
1976年 | 10篇 |
1973年 | 8篇 |
1958年 | 18篇 |
1954年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
吴秋凤 《广东海洋大学学报》2003,23(5):94-98
在阐述西部大开发中科技主导地位的基础上 ,从科技应用成效二重性的视角 ,探讨了关注西部科技伦理的必要性 ,并初步提出了西部大开发战略的科技伦理调控机制 相似文献
42.
1 IntroductionDiscontinuousDeformationAnalysis(DDA)developedbyShiin 1 980’s[1 ,2 ] maybeusedtocalculatethedeformationanddisplacementsinamulti blocksystemandtoanalyzetherelationbe tweenforcesanddisplacementsinthesystem .Ifthesurveydisplacementofeverypointordirectionisknown,alldisplacementsanddeformationsofblocks,eventheglide ,theclosureandthestretchoftheboundary planeofblocks ,canbecalculated .TheresultisoptimallyfittedaccordingtotheLeastSquarePrinciple.DDAismainlyusedinrockblockssystems… 相似文献
43.
44.
CORROSION AND ADHERENCE AT SEA OIL-PLATFORM 总被引:1,自引:0,他引:1
Measurements of the adhesive corrosion and protective potentials of 3 Bohai Sea oilplatforms under different cathodic protection showed corrosion still occurred on these platforms undertheir designed protective potentials. Preliminary conclusions from indoor experiments on the relation betweenadhesive corrosion and cathodic protection showed adhering organisms caused the corrosion onthese platforms. 相似文献
45.
ZHANG Jimin ) LIU Shuang ) SUN Xue ) YANG Guanpin ) ZHANG Xuecheng ) * GAO Zhenhui ) ) North China Sea Monitoring Center SOA Fushun Road Qingdao P..R.China) College of Marine Life Sciences Ocean University of China Qingdao P..R.China 《中国海洋大学学报(英文版)》2003,2(1)
1 Introduction Nannochloropsissp .areoneofpotentialsourcesofpolyunsaturatedfattyacids ,especiallytheeicosapen taentaenoicacid (EPA ,C2 0∶5 ) ,whichisimportantforbothanimalsandhumans . Thefattyacidcompositionofthisalgaisaffectedbyvariousenvironmentalfactors ,suchaslightintensity(Sukeniketal.,1989;Sukeniketal.,1990 ) ,imply ingthatafactorinfluencingthephotosyntheticprocessmayaffectcellularfattyacidsynthesisandtheirmetabolism .AselectionprogramofincreasingcellularEPAcontenthasbeencarriedo… 相似文献
46.
47.
Observation of fluid parcel pathways in the Kuroshio Stream revealed a striking crossstream pattern associated with the Kuroshio‘‘ s meanders. In order to understand the observed pattern, a two-dimensional kinematic model of a meandering jet was developed which could be used to examine the relationship between streamfunction patterns and fluid parcel trajectories. The experiments designed to investigate the dependence of the water exchanges between the Kuroshio water and its surroundings on the characteristics of the Kuroshio‘‘s meanders involved the downstream speed,phase speed and the amplitude of other propagating waves. The results suggested that fluid parcels could cross the meandering jet to and fro; and that the water exchanges between the Kuroshio and its surroundings increased with a) increasing meander amplitude, b) decreasing downstream speed, and c) increasing wave phase speed. The results also showed that when the meandering jet was disturbed by other propagating waves, more effective water exchanges could be induced. 相似文献
48.
For a Hamiltonian that can be separated into N+1(N\geq 2) integrable parts, four algorithms can be built for a symplectic integrator. This research compares these algorithms for the
first and second order integrators. We found that they have similar local truncation errors represented by error Hamiltonian
but rather different numerical stability. When the computation of the main part of the Hamiltonian, H
0, is not expensive, we recommend to use S
* type algorithm, which cuts the calculation of the H
0 system into several small time steps as Malhotra(1991) did. As to the order of the N+1 parts in one step calculation, we found that from the large to small would get a slower error accumulation.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
49.
孙世春 《中国海洋湖沼学报》1995,(2)
Two nemerteans of the Zhoushan Islands, Paranemertes sinensis sp. nov. and P. peregrina, are reportedin this paper. P. sinensis sp. nov. has the body wall longitudinal musculature anteriorly divided,numerous eyes grouped into four clusters, two pairs of cephalic furrows, rhynchocoel 1/3 to 1/2 of fullbody length, cephalic glands well developed and posteriorly extending beyond the cerebral ganglia.precerebral septum absent, cerebral sense organs situated in front of brain, three pairs of nephridiopores,and 17-18 proboscis nerves. 相似文献
50.
广西中三叠统浊流流向及坡向 总被引:1,自引:0,他引:1
通过对广西中三叠统浊积岩系中溢堤流沉积的识别,结合同一鲍马层序Tc段斜层理倾向与其底部槽模走向不一致的分析,以及横向冲刷模、U形障碍冲刷痕等冲蚀构造、大型滑动模等压刻构造的认识,筛选出宽阔水道充填沉积、扇状体及分支水道沉积中底模构造的指向数据,来指示浊流主体流向,并区分出溢堤流流向。从而确定了本区中三叠世时的浊流主体流向为NW向,平均为300°。根据滑塌沉积中滑塌包卷层轴面、滑塌面的测定,确定凤山县金牙处的古坡向平均为322°,与浊流主体流向基本一致。还认为中三叠世时右江盆地沉积物源来自桂东和桂东南蚀源区,海水由其南的越南境内进入。 相似文献