全文获取类型
收费全文 | 40249篇 |
免费 | 1713篇 |
国内免费 | 3500篇 |
专业分类
系统科学 | 4824篇 |
丛书文集 | 964篇 |
教育与普及 | 127篇 |
理论与方法论 | 81篇 |
现状及发展 | 557篇 |
综合类 | 38904篇 |
自然研究 | 5篇 |
出版年
2024年 | 201篇 |
2023年 | 515篇 |
2022年 | 735篇 |
2021年 | 852篇 |
2020年 | 894篇 |
2019年 | 697篇 |
2018年 | 721篇 |
2017年 | 861篇 |
2016年 | 909篇 |
2015年 | 1301篇 |
2014年 | 1924篇 |
2013年 | 1713篇 |
2012年 | 2490篇 |
2011年 | 2501篇 |
2010年 | 1893篇 |
2009年 | 2316篇 |
2008年 | 2137篇 |
2007年 | 2947篇 |
2006年 | 2635篇 |
2005年 | 2395篇 |
2004年 | 2123篇 |
2003年 | 1871篇 |
2002年 | 1595篇 |
2001年 | 1306篇 |
2000年 | 1197篇 |
1999年 | 1090篇 |
1998年 | 817篇 |
1997年 | 799篇 |
1996年 | 677篇 |
1995年 | 563篇 |
1994年 | 499篇 |
1993年 | 454篇 |
1992年 | 398篇 |
1991年 | 357篇 |
1990年 | 344篇 |
1989年 | 249篇 |
1988年 | 217篇 |
1987年 | 129篇 |
1986年 | 67篇 |
1985年 | 26篇 |
1984年 | 11篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 21篇 |
1955年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
徐重阳 《华中科技大学学报(自然科学版)》1987,(1)
本文介绍一种用非晶金属硅化物改善a—Sipin太阳电池TCO/p界面特性的新方法.文章中详细讨论了载流子的传输模型并给出了一系列的实验数据.利用这种方法,用单反应室等离子体CVD装置使a—Si电池的短路电流提高了10%以上,并已获得10.6%的转换效率. 相似文献
42.
43.
《科学通报(英文版)》2006,(5)
QUANTITATIVE STRUCTURE ACTIVITY RELATIONSHIP (QSAR) IS A VERY IMPORTANT TOPIC FOR MANY SCIENTIFIC FIELDS AND CAN BE TERMED AS QUANTITATIVE SEQUENCE ACTIVITY MODELS(QSAM)[1] WHEN REFERRED TO THE RESEARCH ON RELATION- SHIPS BETWEEN STRUCTURES AND ACTIVITIES OF BIOLOGICAL MOLECULES, SUCH AS PROTEINS, AND NUCLEIC ACIDS. HOW- EVER, IT IS VERY DIFFICULT TO ESTABLISH A QSAM MODEL,… 相似文献
44.
分析了局部损伤模型在进行混凝土应变软化模拟时存在的问题:网络依赖性和零能量损耗问题;分别应用隐式梯度模型和局部模型对混凝土应变软化进行了模拟。计算表明该隐式梯度模型可较好避免有限元在应变软化模拟时的网络依赖性,预测出的荷载-位移响应与实际情况吻合较好。 相似文献
45.
Finding finer functions for partially characterized proteins by protein-protein interaction networks
LI YanHui GUO Zheng MA WenCai YANG Da WANG Dong ZHANG Min ZHU ding ZHONG GuoCai LI YongJin YAO Chen WANG Jing 《科学通报(英文版)》2007,52(24):3363-3370
Based on high-throughput data, numerous algorithms have been designed to find functions of novel proteins. However, the effectiveness of such algorithms is currently limited by some fundamental factors, including (1) the low a-priori probability of novel proteins participating in a detailed function; (2) the huge false data present in high-throughput datasets; (3) the incomplete data coverage of functional classes; (4) the abundant but heterogeneous negative samples for training the algorithms; and (5) the lack of detailed functional knowledge for training algorithms. Here, for partially characterized proteins, we suggest an approach to finding their finer functions based on protein interaction sub-networks or gene expression patterns, defined in function-specific subspaces. The proposed approach can lessen the above-mentioned problems by properly defining the prediction range and functionally filtering the noisy data, and thus can efficiently find proteins’ novel functions. For thousands of yeast and human proteins partially characterized, it is able to reliably find their finer functions (e.g., the translational functions) with more than 90% precision. The predicted finer functions are highly valuable both for guiding the follow-up wet-lab validation and for providing the necessary data for training algorithms to learn other proteins. 相似文献
46.
The controlling factors and distribution prediction of H2S formation in marine carbonate gas reservoir, China 总被引:1,自引:0,他引:1
ZHU GuangYou ZHANG ShuiChang LIANG YingBo 《科学通报(英文版)》2007,52(A01):150-163
Generally, there are some anhydrites in carbonate reservoir, as H2S is also familiar in carbonate oil and gas reservoirs. Nowadays, natural gas with high H2S concentration is usually considered as TSR origin, so there is close relationship between H2S and anhydrite. On the contrary, some carbonate rocks with anhydrite do not contain H2S. Recently, researches show that H2S is only a necessary condition of H2S formation. The reservoir porosity, sulfate ion content within formation water, reservoir temperature, oil/gas and water interface, hydrocarbon and some elements of reservoir rock have great controlling effects on the TSR occurrence. TSR deoxidizes hydrocarbon into the acidic gas such as H2S and CO2, and the H2S formation is controlled by TSR occurrence, so the relationship among reaction room, the contact chance of sulfate ion and hydrocarbon, the reservoir temperature has great influence on the TSR reaction. H2S has relatively active chemical quality, so it is still controlled by the content of heavy metal ion. Good conditions of TSR reaction and H2S preservation are the prerequisite of H2S distribu- tion prediction. This paper builds a predictive model based on the characteristic of natural gas reservoir with high H2S-bearing. In the porosity reservoir with anhydrite, the formation water is rich in sulfate and poor in heavy metal ion. Oil and gas fill and accumulate in the gas reservoir with good preservation conditions, and they suffered high temperature later, which indicates the profitable area of natural gas with high H2S-bearing. 相似文献
47.
48.
本文主要求出了J-C系统受与腔场非共振的外场驱动时的准能级及态的近似表达式,设外场与腔模的失谐量△_c远小于耦合常数g,并且腔模光子数较小,在计算中可略去。结果可知,失谐量△_c存在使能级中心位置移动,但对能级分裂量没有影响。相应的光场态为两个位移福克态的叠加。 相似文献
49.
祁明 《陕西师范大学学报(自然科学版)》1992,(2)
在 K-饱和的非标准模型中,研究了泛 Loeb 可测集 m(A),pns(~*X),cpt(~*X),fin(~*X),ns(~*X)的 S-饱和性.当 A 是紧致 Hausdorff 空间 X 的子集时,得到了 st~(-1)(A)是标准集的充分条件. 相似文献
50.
庞乾骏 《上海交通大学学报》1996,30(9):24-29,33
提出了一种掺杂离子导体(DIC)的粒子交叠广义晶格模型,由此模型,推导随机-电阻-网络(RRN)理论中3种导电键各自组分的几率,并采用有效介质近似(EMA)计算了DIC系统的电导及其粒子尺度效应。 相似文献