全文获取类型
收费全文 | 65954篇 |
免费 | 2020篇 |
国内免费 | 1255篇 |
专业分类
化学 | 32734篇 |
晶体学 | 1065篇 |
力学 | 3658篇 |
综合类 | 68篇 |
数学 | 5469篇 |
物理学 | 26235篇 |
出版年
2022年 | 771篇 |
2021年 | 746篇 |
2020年 | 747篇 |
2019年 | 711篇 |
2018年 | 777篇 |
2017年 | 691篇 |
2016年 | 1195篇 |
2015年 | 980篇 |
2014年 | 1347篇 |
2013年 | 2982篇 |
2012年 | 2891篇 |
2011年 | 3661篇 |
2010年 | 2535篇 |
2009年 | 2572篇 |
2008年 | 3210篇 |
2007年 | 3000篇 |
2006年 | 2844篇 |
2005年 | 2562篇 |
2004年 | 2253篇 |
2003年 | 1993篇 |
2002年 | 1888篇 |
2001年 | 3207篇 |
2000年 | 2301篇 |
1999年 | 1707篇 |
1998年 | 1227篇 |
1997年 | 1183篇 |
1996年 | 1019篇 |
1995年 | 928篇 |
1994年 | 812篇 |
1993年 | 724篇 |
1992年 | 1019篇 |
1991年 | 1040篇 |
1990年 | 903篇 |
1989年 | 803篇 |
1988年 | 776篇 |
1987年 | 826篇 |
1986年 | 676篇 |
1985年 | 900篇 |
1984年 | 839篇 |
1983年 | 578篇 |
1982年 | 572篇 |
1981年 | 538篇 |
1980年 | 497篇 |
1979年 | 621篇 |
1978年 | 650篇 |
1977年 | 660篇 |
1976年 | 575篇 |
1975年 | 481篇 |
1974年 | 521篇 |
1973年 | 450篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
901.
L. Bapat G. N. Natu G. Y. Rohokale 《Journal of Radioanalytical and Nuclear Chemistry》1992,165(2):127-136
-Irradiated KCl, KBr and KI are dissolved separately in the emulsion of water and aniline. Halogens as radiolytic products are extracted in aniline forming stable halogen-aniline complexes. Hole species from V2 and V3 centers and free halogens trapped in crystalline salts are solvated first in water phase during dissolution and immediately form complexes with aniline. A typical vibrational structure of absorption bands around 300 nm is observed. The yields of halogens and thereby complexes are found to depend upon the concentration of F and hole centers and the mesh of the salt. 相似文献
902.
Generation of chromioenamines by reduction of O-acetyloximes with chromium(II) and their application
Chromioenamines can be generated by treatment of O-acetyloximes with chromium(II) via two steps of one-electron reduction and successive isomerization, and the species react with aldehydes to give gamma-amino alcohols after reduction with LiAlH4. 相似文献
903.
Y. Oura S. Enomoto H. Nakahara H. Matsue C. Yonezawa 《Journal of Radioanalytical and Nuclear Chemistry》2000,244(2):311-315
Prompt -ray analysis with the internal monostandard method was used to organs taken from rats. After B or Cd was administered, the B/H and Cd/H contents ratios were determined in the brain, kidney, and liver to study their distribution and metabolism. Boron was distributed in all organs but metabolized quickly. Cd was slowly accumulated in the liver and kidneys during the 65 hours studied but no Cd was detected in the brain. 相似文献
904.
E Ohshima T Kumazawa H Takizawa H Harakawa H Sato H Obase Y Oiji A Ishii H Ishii K Ohmori 《Chemical & pharmaceutical bulletin》1991,39(10):2724-2728
A new series of 11-substituted 6,11-dihydrodibenz[b,e]oxepin derivatives was synthesized and evaluated for antiallergic activity. Convenient methods for the preparation of sulfides from alcohols were developed. Structure-activity relationships are described. Compound 7, 11-[2-(dimethylamin)ethyl]thio-6,11-dihydrodibenz[b,e] oxepin-2-carboxylic acid hydrochloride, was the most potent in the rat passive cutaneous anaphylaxis test (ED50 = 0.92 mg/kg p.o.). It had a potent inhibitory effect on anaphylactic bronchoconstriction in guinea pigs (ED50 = 0.029 mg/kg p.o.) and H1 receptor antagonistic effect (Ki = 14 nM) with few central nervous system side effects. Additionally, an antagonistic effect against prostaglandin D2-induced contraction of isolated guinea pig trachea (pA2 = 5.73) was an attractive mechanism of action of the new antiallergic agent. Compound 7 was selected for further evaluation as KW-4994. 相似文献
905.
Isomers of O-alpha-D-glucopyranosyl-(1----6)-O-beta-D-glucopyranosyl- (1----6)-N-[L-aspart-1-oyl-(L-proline)-4-oyl]-alpha-D-glucopyranos ylamine have been prepared, as models for a derivative possibly present in the glomerular basement membrane of rats, by condensation of the corresponding dipeptide derivative (5) with triglycosylamine (4) in the presence of O,O-diethylcyanophosphonate, followed by deprotection of the trisaccharide-dipeptide derivative. During the deprotection process, cis- and trans-isomers containing proline were separated by silica gel column chromatography and also reversed-phase high performance liquid chromatography. 相似文献
906.
Y. L. Tong 《Annals of the Institute of Statistical Mathematics》1987,39(1):289-297
Summary This paper concerns interval estimation of the critical value θ which satisfies
under the general linear model,Y
i
=μ(x
i
)+ε
i
(i=1,2,···), where
for
and the functional forms off
j
′
s are known. From an asymptotic expansion it is shown that, under reasonable conditions, the limiting distribution of
is normal. Thus in the large-sample case a confidence interval for θ can be obtained. Such a result is useful when one is
interested in carrying out a retrospective analysis rather than designing the experiment (as in the Kiefer-Wolfowitz procedure).
In Section 3 a sequential procedure is considered for confidence intervals with fixed width 2d. It is shown that, for a given stopping variableN,
is also asymptotically normal asd→0. Thus the coverage probability converges to 1−α (preassigned) asd→0. An example of application in estimating the phase parameter in circadian rhythms is given for the purpose of illustration.
Research partially supported by the NSF Grant DMS-8502346. 相似文献
907.
We establish some inequalities connecting natural parameters of a partial order P. For example, if every interval [a,b] contains at most maximal chains, if some antichain has cardinality v, and if there are 1 chains whose union is cofinal and coinitial in P, then the chain decomposition number for P is 1v (Theorem 2.2), and the inequality is sharp in a certain sense (Section 3).This paper was written while the authors were visitors at the Laboratoire d'algèbre ordinale, Département de Mathématiques, Université Claude Bernard, Lyon 1, France.Research supported by NSERC grant # A5198. 相似文献
908.
A. Y. Lee 《Journal of Optimization Theory and Applications》1987,52(1):151-162
Bounded terminal conditions of nonlinear optimization problems are converted to equality terminal conditions via the Valentine's device. In so doing, additional unknown parameters are introduced into the problem. The transformed problems can still be easily solved using the sequential gradient-restoration algorithm (SGRA) via a simple augmentation of the unknown parameter vector . Three example problems with bounded terminal conditions are solved to verify this technique.This research was supported in part by the National Aeronautics and Space Administration under NASA Grant No. NCC 2-106. 相似文献
909.
Y. Kazama 《Czechoslovak Journal of Physics》1987,37(3):312-328
A pedagogical account is given of the recent developments in covariant (super)string field theories. After reviewing the construction of the free open bosonic string field theory, the super-symmetric case is treated and the space-time supersymmetry transformations are explained. The present status and some future problems are also summarized.Invited talk presented at the International Conference Selected Topics in Quantum Field Theory and Mathematical Physics, Bechyn, Czechoslovakia, June 23–27, 1986.On leave of absence fromNational Laboratory for High Energy Physics (KEK), Tsukuba, Ibaraki, Japan.I would like to thank A. Neveu, H. Nicolai and P. West for many discussions, and the CERN Theoretical Physics Division for hospitality and generous support. 相似文献
910.
A.C. and d.c. electrical conductivities, thermoelectric power and dielectric constant of copper vanadate (CuV2O6) have been measured in the temperature range 300–1000 K in order to discuss the electrical conduction in the compound. The extrinsic conduction, which takes place below 500 K, has been explained by small polaron hopping mechanism while intrinsic conduction, which takes place above 500 K, has been explained by large polaron band mechanism in view of the values of activation energy and charge carrier mobility in the temperature ranges 300–500 K and 500–1000 K. 相似文献