全文获取类型
收费全文 | 9741篇 |
免费 | 169篇 |
国内免费 | 38篇 |
专业分类
化学 | 6032篇 |
晶体学 | 131篇 |
力学 | 327篇 |
数学 | 1085篇 |
物理学 | 2373篇 |
出版年
2021年 | 52篇 |
2020年 | 83篇 |
2019年 | 89篇 |
2017年 | 58篇 |
2016年 | 105篇 |
2015年 | 106篇 |
2014年 | 148篇 |
2013年 | 444篇 |
2012年 | 343篇 |
2011年 | 416篇 |
2010年 | 216篇 |
2009年 | 242篇 |
2008年 | 403篇 |
2007年 | 423篇 |
2006年 | 428篇 |
2005年 | 401篇 |
2004年 | 359篇 |
2003年 | 315篇 |
2002年 | 302篇 |
2001年 | 196篇 |
2000年 | 216篇 |
1999年 | 120篇 |
1998年 | 104篇 |
1997年 | 109篇 |
1996年 | 147篇 |
1995年 | 130篇 |
1994年 | 176篇 |
1993年 | 181篇 |
1992年 | 180篇 |
1991年 | 121篇 |
1990年 | 126篇 |
1989年 | 135篇 |
1988年 | 106篇 |
1987年 | 130篇 |
1986年 | 119篇 |
1985年 | 206篇 |
1984年 | 165篇 |
1983年 | 118篇 |
1982年 | 144篇 |
1981年 | 137篇 |
1980年 | 157篇 |
1979年 | 146篇 |
1978年 | 141篇 |
1977年 | 120篇 |
1976年 | 134篇 |
1975年 | 121篇 |
1974年 | 139篇 |
1973年 | 133篇 |
1972年 | 62篇 |
1971年 | 66篇 |
排序方式: 共有9948条查询结果,搜索用时 62 毫秒
91.
Smith K. D. Klasson K. T. Clausen Ackerson E. C. Gaddy J. L. 《Applied biochemistry and biotechnology》1991,28(1):787-796
Applied Biochemistry and Biotechnology - The results of this study support the hypothesis that several organisms that are capable of utilizing CO are also capable of degrading CO-like compounds,... 相似文献
92.
Kazufumi Takahashi Raymond N. Castle Milton L. Lee 《Journal of heterocyclic chemistry》1987,24(4):977-979
The four acridinecarbaldehydes, namely, acridine-1-carbaldehyde, acridine-2-carbaldehyde, acridine-3-carbaldehyde, and acridine-4-carbaldehyde have been synthesized for the first time. 相似文献
93.
INDUCIBLE POSTREPLICATION REPAIR IS RESPONSIBLE FOR MINIMAL MEDIUM RECOVERY IN UV-IRRADIATED Escherichia coliK–12 总被引:1,自引:0,他引:1
Abstract— Ultraviolet (UV)-irradiated Escherichia coli K–12 uvrA cells showed higher survival if plated on minimal growth medium rather than on rich growth medium, i.e., they showed minimal medium recovery (MMR). A 2-hour treatment of UV-irradiated cells with rifampicin inhibited the subsequent expression of MMR, and produced a large reduction in survival. We have recently isolated a new mutant ( mmrA1 ) that does not show MMR. The mmrA mutation protected UV-irradiated uvrA cells from the effect of rich growth medium on survival, but not from the effect of rifampicin on survival. DNA daughter-strand gap (DSG) repair in UV-irradiated (4 J/m2 ) uvrA cells was inhibited to the same degree whether rich growth medium was added immediately after irradiation or after 10 min of postirradiation incubation in minimal growth medium. However, chloramphenicol added immediately after irradiation greatly reduced this repair; there was less reduction if it was added 10 min after UV irradiation. These findings suggest that MMR is an inducible repair phenomenon, and that rich growth medium inhibits this repair process itself rather than its induction. 相似文献
94.
Anzalone PW Baru AR Danielson EM Hayes PD Nguyen MP Panico AF Smith RC Mohan RS 《The Journal of organic chemistry》2005,70(6):2091-2096
[reaction: see text] Three one-pot methods for the conversion of aldehydes to homoallyl ethers catalyzed by Bi(OTf)(3).xH(2)O (1 < x < 4) have been developed. The one-pot synthesis of homoallyl ethers can be achieved either by in situ generation of the acetal followed by its reaction with allyltrialkylsilane or by a three-component synthesis in which the aldehyde, trimethylorthoformate or an alkoxytrimethylsilane and allyltrimethylsilane are mixed together in the presence of bismuth triflate (0.1-1.0 mol %). In addition, a three-component synthesis of homoallyl acetates, which is achieved by reacting the aldehyde, acetic anhydride, and allyltrimethylsilane in the presence of bismuth triflate (3.0-5.0 mol %), has been developed. The use of a relatively nontoxic, easy to handle, and inexpensive catalyst adds to the versatility of these methods. 相似文献
95.
Simulation of aerated lagoon using artificial neural networks and multivariate regression techniques
Karla Patricia Oliveira-Esquerre Aline C. da Costa Roy Edward Bruns Milton Mori 《Applied biochemistry and biotechnology》2003,106(1-3):437-449
The aim of this study was to develop an empirical model that provides accurate predictions of the biochemical oxygen demand
of the output stream from the aerated lagoon at International Paper of Brazil, one of the major pulp and paper plants in Brazil.
Predictive models were calculated from functional link neural networks (FLNNs), multiple linear regression, principal components
regression, and partial least-squares regression (PLSR). Improvement in FLNN modeling capability was observed when the data
were preprocessed using the PLSR technique. PLSR also proved to be a powerful linear regression technique for this problem,
which presents operational data limitations. 相似文献
96.
Two organoaluminium amides have been used to initiate the polymerizations of methyl methacrylate, acetaldehyde and n-butyraldehyde. Methyl methacrylate polymerized through the vinyl function to give amorphous products. The aldehydes reacted through the carbonyl group at low temperatures with high degrees of stereospecificity to give polymers with substantial crystallinity. The molecular weight of the polyacetaldehyde is very high. 相似文献
97.
98.
99.
100.
S. F. Biagi M. Bourquin R. M. Brown H. J. Burckhart P. Extermann M. Gailloud C. N. P. Gee W. M. Gibson P. Jacot-Guillarmod J. Perrier K. J. Ragan Ph. Rosselet P. Schirato H. W. Siebert V. J. Smith K. P. Streit J. J. Thresher A. T. Wood C. Yanagisawa 《Zeitschrift fur Physik C Particles and Fields》1987,34(2):175-185
In an experiment at the CERN-SPS charged hyperon beam, we have investigated the inclusive \(\Lambda \bar K^0 \) and \(\Sigma ^0 \bar K^0 \) final states formed in Ξ? Be interactions. In the \(\Lambda \bar K^0 \) channel, we observe a signal at 1826 MeV/c2 which can be identified with the known Ξ(1820) resonance. We determine its mass and width to be:M=1826±4 MeV/c2, Г=12±14 MeV/c2. A moment analysis is consistent with a spin of 3/2 and indicates a negative parity for this spin assignment. Also in the \(\Lambda \bar K^0 \) channel, we observe a 3.6σ signal with the following parameters:M=1963±5 MeV/c2, Г=25±15 MeV/c2. This state, which we call Ξ(1960), is not observed in the \(\Sigma ^0 \bar K^0 \) channel, leading to an upper limit on the ratio of partial widths \(\Sigma \bar K/\Lambda \bar K\) of 2.3 (90% confidence level). A moment analysis of the \(\Lambda \bar K^0 \) final state indicates a spin of 5/2 or greater in the natural spin-parity series 5/2+, 7/2?, etc. 相似文献