全文获取类型
收费全文 | 36451篇 |
免费 | 293篇 |
国内免费 | 328篇 |
专业分类
化学 | 15857篇 |
晶体学 | 333篇 |
力学 | 1555篇 |
综合类 | 12篇 |
数学 | 9757篇 |
物理学 | 9558篇 |
出版年
2021年 | 76篇 |
2020年 | 103篇 |
2019年 | 131篇 |
2018年 | 1261篇 |
2017年 | 1497篇 |
2016年 | 850篇 |
2015年 | 668篇 |
2014年 | 609篇 |
2013年 | 975篇 |
2012年 | 3527篇 |
2011年 | 2829篇 |
2010年 | 2034篇 |
2009年 | 1738篇 |
2008年 | 1002篇 |
2007年 | 1113篇 |
2006年 | 1112篇 |
2005年 | 4898篇 |
2004年 | 4349篇 |
2003年 | 2644篇 |
2002年 | 817篇 |
2001年 | 419篇 |
2000年 | 217篇 |
1999年 | 272篇 |
1998年 | 201篇 |
1997年 | 156篇 |
1996年 | 164篇 |
1995年 | 121篇 |
1994年 | 117篇 |
1993年 | 101篇 |
1992年 | 249篇 |
1991年 | 220篇 |
1990年 | 204篇 |
1989年 | 164篇 |
1988年 | 170篇 |
1987年 | 118篇 |
1986年 | 94篇 |
1985年 | 116篇 |
1984年 | 107篇 |
1983年 | 99篇 |
1982年 | 86篇 |
1981年 | 82篇 |
1980年 | 75篇 |
1979年 | 93篇 |
1978年 | 98篇 |
1977年 | 81篇 |
1976年 | 144篇 |
1975年 | 86篇 |
1974年 | 86篇 |
1973年 | 93篇 |
1972年 | 51篇 |
排序方式: 共有10000条查询结果,搜索用时 328 毫秒
21.
Sándor G?r?g 《Analytical sciences》2004,20(5):767-782
The development during the last 15 years and the state-of-the-art in the analysis of bulk steroid hormone drugs and hormone-like structures and pharmaceutical formulations made thereof are summarized. Other steroids (sterols, bile acids, cardiac glycosides, vitamins D) as well as biological-clinical aspects and pharmacokinetic and metabolic studies are excluded from this review. The state-of-the-art is summarized based on comparisons of monographs in the latest editions of the European Pharmacopoeia, United States Pharmacopoeia and the Japanese Pharmacopoeia. This is followed by sections dealing with new developments in the methodology for the fields of spectroscopic and spectrophotometric, chromatographic, electrophoretic and hyphenated techniques as well electroanalytical methods. The review is terminated by two problem-oriented sections: examples on impurity and degradation profiling as well as enantiomeric analysis. 相似文献
22.
The electrochemical reduction of 1-([(4-halophenyl)imino]methyl)-2-naphthols on graphite electrodes was studied using cyclic voltammetry, chronoamperometry, constant-potential coulometry and preparative constant-potential electrolysis techniques. The data revealed that the reduction on graphite was irreversible and followed an EC mechanism. The diffusion coefficients and the number of electrons transferred were determined using the chronoamperometric Cottrell slope and the ultramicro disc Pt-electrode steady-state current. The number of electrons was also determined by bulk electrolysis. The compounds were subjected to constant-potential preparative electrolysis and the electrolysis products were purified and identified by spectroscopic methods. Based on these findings, a mechanism for the electro-reduction process is proposed. 相似文献
23.
JingXiaWANG ChengYouKAN DeShanLIU 《中国化学快报》2004,15(10):1161-1163
Two novel polymerizable dyes with anthraquinone residue have been prepared, and their structures were characterized by FTIR, ^1HNMR and EA. 相似文献
24.
25.
Paramagnetic pyrroline and 1,2,3,6-tetrahydropyridine derivatives of BODIPY and their diamagnetic analogs have been synthesized and characterized as novel redox double sensor and cation sensitive reagents. 相似文献
26.
Gerald Moore. 《Mathematics of Computation》2004,73(245):211-242
We present an algorithm, based on approximation by Laguerre polynomials, for computing a point on the stable manifold of a stationary solution of an autonomous system. A superconvergence phenomenon means that the accuracy of our results is much higher than the usual spectral accuracy. Both the theory and the implementation of the method are considered. Finally, as an application of the algorithm, we describe a fully spectral approximation of homo- and heteroclinic orbits.
27.
28.
We prove that RANDOM EDGE, the simplex algorithm that always chooses a random improving edge to proceed on, can take a mildly exponential number of steps in the model of abstract objective functions (introduced by Williamson Hoke [Completely unimodal numberings of a simple polytope, Discrete Appl. Math. 20 (1988) 69-81.] and by Kalai [A simple way to tell a simple polytope from its graph, J. Combin. Theory Ser. A 49(2) (1988) 381-383.] under different names). We define an abstract objective function on the n-dimensional cube for which the algorithm, started at a random vertex, needs at least exp(const·n1/3) steps with high probability. The best previous lower bound was quadratic. So in order for RANDOM EDGE to succeed in polynomial time, geometry must help. 相似文献
29.
30.
The Bekenstein–Hawking entropy of certain black holes can be computed microscopically in string theory by mapping the elusive
problem of counting microstates of a strongly gravitating black hole to the tractable problem of counting microstates of a
weakly coupled D-brane system, which has no event horizon, and indeed comfortably fits on the head of a pin. We show here
that, contrary to widely held beliefs, the entropy of spherically symmetric black holes can easily be dwarfed by that of stationary
multi-black-hole “molecules” of the same total charge and energy. Thus, the corresponding pin-sized D-brane systems do not
even approximately count the microstates of a single black hole, but rather those of a zoo of entropically dominant multicentered
configurations.
Fourth Award in the 2007 Essay Competition of the Gravity Research Foundation. 相似文献