全文获取类型
收费全文 | 13242篇 |
免费 | 287篇 |
国内免费 | 46篇 |
专业分类
化学 | 7868篇 |
晶体学 | 166篇 |
力学 | 408篇 |
数学 | 1474篇 |
物理学 | 3659篇 |
出版年
2022年 | 100篇 |
2021年 | 115篇 |
2020年 | 154篇 |
2019年 | 159篇 |
2018年 | 132篇 |
2017年 | 108篇 |
2016年 | 207篇 |
2015年 | 177篇 |
2014年 | 234篇 |
2013年 | 658篇 |
2012年 | 547篇 |
2011年 | 648篇 |
2010年 | 364篇 |
2009年 | 368篇 |
2008年 | 592篇 |
2007年 | 603篇 |
2006年 | 620篇 |
2005年 | 544篇 |
2004年 | 448篇 |
2003年 | 407篇 |
2002年 | 384篇 |
2001年 | 266篇 |
2000年 | 283篇 |
1999年 | 159篇 |
1998年 | 140篇 |
1997年 | 139篇 |
1996年 | 185篇 |
1995年 | 165篇 |
1994年 | 210篇 |
1993年 | 232篇 |
1992年 | 210篇 |
1991年 | 153篇 |
1990年 | 166篇 |
1989年 | 168篇 |
1988年 | 139篇 |
1987年 | 158篇 |
1986年 | 139篇 |
1985年 | 234篇 |
1984年 | 193篇 |
1983年 | 141篇 |
1982年 | 161篇 |
1981年 | 157篇 |
1980年 | 178篇 |
1979年 | 166篇 |
1978年 | 169篇 |
1977年 | 148篇 |
1976年 | 167篇 |
1975年 | 146篇 |
1974年 | 167篇 |
1973年 | 163篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
An improved high-performance liquid chromatographic method for the simultaneous determination of caffeine and its N-demethylated metabolites in plasma is described. Excellent resolution of all components is provided by reversed-phase chromatography using a mobile phase consisting of 1% acetic acid-methanol (83:17) at a flow-rate of 2.7 ml/min, in conjunction with a Waters Assoc. Nova-Pak C18 column which was protected by a Waters Assoc. Guard-Pak precolumn module containing a Guard-Pak CN cartridge. Rapid extraction of caffeine and the dimethylxanthines from plasma was achieved using reversed-phase octadecylsilane bonded-silica columns (Bond-Elut C18). With only 100 microliters of sample, plasma levels in the region of 50 ng/ml for the dimethylxanthines and 100 ng/ml for caffeine can be determined using ultraviolet detection at 273 nm. The method has been used for measuring umbilical cord plasma samples to provide information regarding foetal exposure to caffeine and its metabolites and is also suitable for therapeutic drug monitoring of caffeine and theophylline levels in the treatment of neonatal apnoea. 相似文献
92.
93.
David Kessel Kevin M. Smith R. K. Pandey F.-Y. Shiau Barbara Henderson 《Photochemistry and photobiology》1993,58(2):200-203
Abstract— Biophysical and photobiological properties of a group of bacteriochlorins were compared with efficacy of these products for photodynamic therapy of murine tumors. Predictive factors for selective photosensitization in vivo include affinity binding to lipoproteins greater than albumin, extinction coefficient at the wavelength of irradiation and tumor/skin distribution. Efficacy was correlated with circulating plasma levels of the different sensitizers but not with the photodynamic therapy response in cell culture. 相似文献
94.
95.
THE SYNERGISTIC ACTION OF ULTRAVIOLET AND X RADIATION ON MUTANTS OF ESCHERICHIA COLI K-12 总被引:1,自引:0,他引:1
Abstract— Prior UV irradiation increased the X-ray sensitivity of wild-type E. coli K-12. This synergistic effect of combined UV and X irradiation was also observed, but to a reduced extent, in uvrA, uvrB, uvrC , and polA mutants, but was absent in exrA, recA, recB , or recC mutants of E. coli K-12. Alkaline sucrose gradient studies demonstrated that the wand err gene-controlled, growth-medium-dependent (Type III) repair of X-ray-induced DNA single-strand breaks was inhibited by prior UV irradiation. This inhibition probably explains the synergistic effect of these two radiations on survival. 相似文献
96.
Film of nylon-6 has been γ-irradiated in vacuo to various doses D. Grafting has been effected by subsequent exposure in vacuo to vapour at 50° of composition 9.1 wt% acrylic acid and 90.9 wt% water. Determinations have been made of total vapour uptake as well as the individual swellings due to monomer and water. For D ? ca. 2 Mrad, the initial rate of grafting Rg increased with D in accord with Rg ∝ Dβ with β = 0.45 ± 0.05, thus suggesting bimolecular chain termination. However, for D ? ca. 2 Mrad, there is no further increase in Rg. This is attributed in part to the fact that the radical yield is proportional to dose only for D ? ca. 2.5 Mrad. Diffusion controlled grafting has been predicted elsewhere to be characterized by β = 0.67. Grafting proceeds from the surface and the initial stages are concluded to be essentially free from diffusion control, since (a) β ≠ 0.67, (b) the rate of uptake of monomer vapour >Rg and (c) a large change in film thickness yields only a very small change in Rg. 相似文献
97.
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
98.
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
99.
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
100.