全文获取类型
收费全文 | 87055篇 |
免费 | 2320篇 |
国内免费 | 4191篇 |
专业分类
化学 | 30976篇 |
晶体学 | 1215篇 |
力学 | 7617篇 |
综合类 | 639篇 |
数学 | 33561篇 |
物理学 | 19558篇 |
出版年
2023年 | 98篇 |
2022年 | 382篇 |
2021年 | 341篇 |
2020年 | 329篇 |
2019年 | 343篇 |
2018年 | 10684篇 |
2017年 | 10721篇 |
2016年 | 6349篇 |
2015年 | 1348篇 |
2014年 | 875篇 |
2013年 | 1057篇 |
2012年 | 4452篇 |
2011年 | 11227篇 |
2010年 | 6459篇 |
2009年 | 6894篇 |
2008年 | 7593篇 |
2007年 | 9604篇 |
2006年 | 1085篇 |
2005年 | 2082篇 |
2004年 | 2095篇 |
2003年 | 2419篇 |
2002年 | 1452篇 |
2001年 | 699篇 |
2000年 | 768篇 |
1999年 | 412篇 |
1998年 | 341篇 |
1997年 | 247篇 |
1996年 | 306篇 |
1995年 | 217篇 |
1994年 | 172篇 |
1993年 | 192篇 |
1992年 | 152篇 |
1991年 | 117篇 |
1990年 | 115篇 |
1989年 | 131篇 |
1988年 | 124篇 |
1987年 | 120篇 |
1986年 | 102篇 |
1985年 | 82篇 |
1984年 | 72篇 |
1983年 | 66篇 |
1982年 | 66篇 |
1981年 | 64篇 |
1980年 | 62篇 |
1979年 | 55篇 |
1978年 | 44篇 |
1914年 | 45篇 |
1912年 | 40篇 |
1909年 | 41篇 |
1908年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
In order to reduce infant mortality in the municipality of Rio de Janeiro it is desired to encourage all mothers-to-be to attend the appropriate health care facilities. A 3-level hierarchical prenatal–neonatal health care system is described together with a basic model for optimising accessibility to facilities. A genetic algorithm to solve the basic model is developed and some numerical experience reported. Extensions to the basic model and planned future research are briefly indicated. 相似文献
92.
Florin Ambro 《manuscripta mathematica》2003,111(1):43-49
We prove a precise inversion of adjunction formula for the log variety (ℂ
d
+1,X), where X is a non-degenerate hypersurface. As a corollary, the minimal log discrepancies of non-degenerate normal hypersurface singularities
are bounded by dimension.
Received: 17 September 2002 / Revised version: 22 November 2002
Published online: 14 February 2003
Current address: DPMMS, CMS, University of Cambridge, Wilberforce Road, Cambridge CB3 0WB, England. e-mail: f.ambro@dpmms.cam.ac.uk
Mathematics Subject Classification (2000): Primary 14B05; Secondary 14M25, 52B20 相似文献
93.
In this paper, we use weighted modules ω(?)(f,t)w to study the pointwise approximation on Szasz-type operators, and obtain the direct and converse theorem, as well as characterizations of the pointwise approximation of Jacobi-weighted Szasz-type operators. 相似文献
94.
Christiane Albrecht 《Analytical and bioanalytical chemistry》2008,390(5):1223-1224
95.
96.
Chengzhi Qi Mingyang Wang Qihu Qian Jianjie Chen 《Moscow University Mechanics Bulletin》2008,63(5):113-121
The formation mechanisms for the structural hierarchy in geological media are discussed. It is shown that the formation of such a hierarchy is caused by certain external and internal circumstances. The first ones consist in the fact that, because of external actions, the Earth’s poles continuously execute the translational and rotational motions responsible for a regular structure of rock fracture and for the appearance of the scale factor √2. The second ones consist in the fact that, under the action of many random factors and because of external actions, during the formation of geological media there appear dissipative structures and, hence, some self-similar fractal structures are formed. 相似文献
97.
M C Testik J K Cochran G C Runger 《The Journal of the Operational Research Society》2004,55(3):233-239
We study the short-term staffing problem of systems that experience random, non-stationary demand. The typical method to accommodate changes in arrival rate is to use historical data to identify peak periods and associated forecasting for upcoming time windows. In this paper, we develop a method that instead detects change as it happens. Motivated by an automatic call distributor system in a call centre with time-varying arrivals, we propose a change detection algorithm based upon non-homogeneous Poisson processes. The proposed method is general and may be thought of as a feed-forward strategy, in which we detect a change in the arrival process, estimate the new magnitude of the arrival rate, and assign an appropriate number of servers to the tasks. The generalized likelihood ratio statistic is used and a recommendation for its decision limit is developed. Simulation results are used to evaluate the performance of the detector in the context of a telephone call centre. 相似文献
98.
This paper considers a receiver set partitioning and sequencing problem in a wavelength division multiplexing single-hop lightwave network for multicasting traffic. The problem is analysed in the approach of uncapacitated single batch-processing machine scheduling. In the analysis, several solution properties are characterized with respect to a mean flow time measure, based upon which two heuristic algorithms are developed, along with a dynamic programming algorithm. Several numerical experiments show that the heuristic algorithms generate good schedules. The problem is extended to consider two measures simultaneously including the mean flow time and the number of transmissions, for which the proposed algorithms also perform well. 相似文献
99.
100.
Flávio A. Pavan Yoshitaka Gushikem Celso C. Moro Tania M. Costa Edilson V. Benvenutti 《Colloid and polymer science》2003,281(2):173-177
Anilinepropylsilica xerogel was obtained by using an appropriate organosilane and tetraethyl orthosilicate as precursor reagents. The gelation was carried out using HF and NaF as catalysts. The presence of Na+ (when NaF was used) resulted in a decrease in the final organic content of the materials. This effect was interpreted as an inhibition of the organosilane polycondensation possibly due to the Na+ interaction with the SiO- groups of the hydrolyzed organosilane. The presence of Na+ also results in morphological changes in the xerogels. 相似文献