全文获取类型
收费全文 | 16596篇 |
免费 | 3441篇 |
国内免费 | 4448篇 |
专业分类
测绘学 | 1591篇 |
大气科学 | 3382篇 |
地球物理 | 4345篇 |
地质学 | 8019篇 |
海洋学 | 2769篇 |
天文学 | 578篇 |
综合类 | 1699篇 |
自然地理 | 2102篇 |
出版年
2024年 | 92篇 |
2023年 | 305篇 |
2022年 | 836篇 |
2021年 | 1028篇 |
2020年 | 807篇 |
2019年 | 924篇 |
2018年 | 965篇 |
2017年 | 865篇 |
2016年 | 997篇 |
2015年 | 907篇 |
2014年 | 1025篇 |
2013年 | 1144篇 |
2012年 | 1046篇 |
2011年 | 1124篇 |
2010年 | 1099篇 |
2009年 | 1034篇 |
2008年 | 929篇 |
2007年 | 906篇 |
2006年 | 779篇 |
2005年 | 718篇 |
2004年 | 532篇 |
2003年 | 447篇 |
2002年 | 483篇 |
2001年 | 528篇 |
2000年 | 479篇 |
1999年 | 628篇 |
1998年 | 522篇 |
1997年 | 501篇 |
1996年 | 475篇 |
1995年 | 372篇 |
1994年 | 352篇 |
1993年 | 328篇 |
1992年 | 271篇 |
1991年 | 220篇 |
1990年 | 172篇 |
1989年 | 152篇 |
1988年 | 130篇 |
1987年 | 59篇 |
1986年 | 73篇 |
1985年 | 42篇 |
1984年 | 37篇 |
1983年 | 19篇 |
1982年 | 39篇 |
1981年 | 13篇 |
1980年 | 18篇 |
1979年 | 15篇 |
1978年 | 7篇 |
1977年 | 6篇 |
1962年 | 5篇 |
1958年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 16 毫秒
81.
Under the artificial condition the 59Fe morphology in sea water, its concentration in sediment and phytoplankton, its distribution and metabolism in tissue organs of marine animals were studied. The results showed that the morphology of 59Fe was in a particulate state in sea water. The adsorption rule of 59Fe by three kinds of sediments was similar. The concentration ability of 59Fe by phytoplankton was very strong. The critical concentration organs of S9Fe by marine animals were viscera. The gross radioactivity of 59Fe was mainly concentrated in protein. The concentration factor of 59Fe by DNA was the highest one. After excretion experiment, 59Fe of all the tissue organs was not detected. Small part of59Fe remained in the organic acid and protein state. There was a redistribution process in sediment for59Fe. 相似文献
82.
83.
九龙江河口区水体中的226Ra和228Ra 总被引:8,自引:0,他引:8
用MnO2-纤维富集大体积水样中的Ra同位素,并用直接射气法测定226Ra和228Ac的β计数法测定228Ra的方法,研究了九龙江河口区226Ra,228Ra的行为,结果表明:在该河口区226Ra,228Ra均呈非保守行为,226Ra,228Ra的最高值分别在盐度为19和9处测得。228Ra/226Ra)A.R.值在盐度小于19的区域约为3左右。与世界其他河口区相比,九龙江河口区的226Ra,22 相似文献
84.
Modelling nitrogen and phosphorus cycles and dissolved oxygen in the Zhujiang Estuary Ⅰ. Model development 总被引:1,自引:0,他引:1
wrmcrloxHuman activities related to the population growth and developrnent of industry and rnwhci-pality have led to the incrouing hadings of various POllutants into estudries during the past fewdecades. These increasing edlutant lOadings have caused declined estuallne hedth which can bemereured by a vdriety of indices. In order to obtain solutions to environrnent problerns, re-sources manageTnnt apencies are supporting a holistic approach to envirorirnental management.An effcient strategy t… 相似文献
85.
符合药用质量要求的甲壳素精制工艺 总被引:3,自引:0,他引:3
本文探讨了符合以下药用质量要求的甲壳素的精制工艺,甲壳素脱乙酰度在70-90%之间,钙的含量〈0.5%,总蛋含量在7-8%之间,灰分〈1%,酸不溶性灰分〈0.05%,无毒,为甲壳素在医药上的应用,提供了生产数据。 相似文献
86.
根据湍流封闭理论,建立一种适用于正压浅海湍流运动的雷诺应力封闭模型(RSM),以代替目前三维浅海动力学模型中普遍采用的湍粘性系数的传统假设。通过直接建立并模化f—平面上正压海洋的雷诺应力传输方程,分别得到的微分形式和代数形式的RSM方程组。并讨论了进行数值计算所需要的边界条件。利用该模型可以进一步研究浅海潮流、风暴潮流及风海流等浅海流动的三维结构和湍流特性。 相似文献
87.
本文介绍的基岩水下爆破属临近重要建筑物的水下控制爆破。当岩石裂隙发育,且岩面有较厚的石碴覆盖层,其技术难度大,采取的诸如搭钢平台钻孔。塑料套管护孔,以及孔间、排间塑料导爆管雷管接力式微差起爆网路等措施,都是成功之经验,值得今后类似工程推广应用。 相似文献
88.
An infinity of conservation laws of fKdV equation is derived in terms of the Miura and Gardner''s transform.The pseudo-mass and energy theorems are studied by the first two conservation laws.As a typical example,the theoretical mean wave resistance and the regional distribution of energy of the precursor soliton generation are determined by means of the first and the second conservation laws. 相似文献
89.
北黄海沉积物——水界面反硝化速率及影响因素研究 总被引:4,自引:0,他引:4
探讨近海氮的循环机制,采用乙炔抑制法和现场静态箱法对北黄海夏季局部海域的反硝化速率进行了研究,该海域反硝化速率在2.5~5.8μmol/m2.h之间,平均4.85μmol/m2.h。影响其反硝化速率的主要因素为溶解氧,其次是温度。北黄海的反硝化速率低于珠江口和长江口海域。 相似文献
90.
The mixing characteristics of particles such as dredged sediment of variable size discharged into cross flow are studied by a 3D numerical model, which is developed to model the particle-fluid two-phase flow. The Eulerian method with the modified k-ε parameterization of turbulence for the fluid phase is used to solve fluid phase, while a Lagrangian method for the solid phase (particles), both the processes are coupled through the momentum sources. In the model the wake turbulence induced by particles has been included as additional source term in the k-ε model; and the variable drift velocities of the particles are treated efficiently by the Lagrangian method in which the particles are tracked explicitly and the diffusion process is approximated by a random walk model. The hydrodynamic behavior of dumping a cloud of particles is governed by the total buoyancy of the cloud, the drag force on each particle and the velocity of cross-flow. The computed results show a roughly linear relationship between the displacement of the frontal position and the longitudinal width of the particle cloud. The particle size in the cloud and the velocity of cross flow dominate the flow behavior. The computed results are compared with the results of laboratory experiments and satisfactory agreement is obtained. 相似文献