全文获取类型
收费全文 | 7243篇 |
免费 | 710篇 |
国内免费 | 668篇 |
出版年
2023年 | 97篇 |
2022年 | 105篇 |
2021年 | 148篇 |
2020年 | 166篇 |
2019年 | 210篇 |
2018年 | 232篇 |
2017年 | 208篇 |
2016年 | 219篇 |
2015年 | 251篇 |
2014年 | 307篇 |
2013年 | 412篇 |
2012年 | 258篇 |
2011年 | 361篇 |
2010年 | 285篇 |
2009年 | 416篇 |
2008年 | 371篇 |
2007年 | 403篇 |
2006年 | 360篇 |
2005年 | 348篇 |
2004年 | 310篇 |
2003年 | 255篇 |
2002年 | 232篇 |
2001年 | 161篇 |
2000年 | 176篇 |
1999年 | 188篇 |
1998年 | 145篇 |
1997年 | 174篇 |
1996年 | 138篇 |
1995年 | 131篇 |
1994年 | 127篇 |
1993年 | 134篇 |
1992年 | 112篇 |
1991年 | 104篇 |
1990年 | 93篇 |
1989年 | 115篇 |
1988年 | 103篇 |
1987年 | 80篇 |
1986年 | 65篇 |
1985年 | 89篇 |
1984年 | 78篇 |
1983年 | 65篇 |
1982年 | 103篇 |
1981年 | 62篇 |
1980年 | 57篇 |
1979年 | 44篇 |
1978年 | 38篇 |
1977年 | 18篇 |
1976年 | 15篇 |
1975年 | 11篇 |
1974年 | 19篇 |
排序方式: 共有8621条查询结果,搜索用时 15 毫秒
21.
Abstract Previous studies employing a single strain of the photosynthetic bacterium Rhodopseudomonas capsulata have demonstrated that this organism, which normally is not capable of growth on glycerol, can gain glycerol-utilizing ability through mutational events. We have examined other strains of R. capsulata of divergent geographic origin, and have found that they could also be converted to a glycerol-catabolic phenotype. Mutant derivatives were found to express high constitutive levels of glycerophosphate dehydrogenase (GPD) and glycerokinase (GK) which were barely detectable in the parental strains. These results suggest that the ability to utilize glycerol after undergoing a gain of function mutation is a widespread property of R. capsulata . 相似文献
22.
23.
24.
Xiuyun Ye Shigeru Yoshida T. B. Ng 《The international journal of biochemistry & cell biology》2000,32(11-12)
A mild and rapid method is described for isolating various milk proteins from bovine rennet whey. β-Lactoglobulin from bovine rennet whey was easily adsorbed on and desorbed from a weak anion exchanger, diethylaminoethyl-Toyopearl. However, α-lactalbumin could not be adsorbed onto the resin. α-Lactalbumin and β-lactoglobulin from rennet whey could also be adsorbed and separated using a strong anion exchanger, quaternary aminoethyl-Toyopearl. The rennet whey was passed through a strong cation exchanger, sulphopropyl-Toyopearl, to separate lactoperoxidase and lactoferrin. α-Lactalbumin and β-lactoglobulin were adsorbed onto quaternary aminoethyl-Toyopearl. α-Lactalbumin was eluted using a linear (0–0.15 M) concentration gradient of NaCl in 0.05 M Tris–HCl buffer (pH 8.5). Subsequently, β-lactoglobulin B and β-lactoglobulin A were eluted from the column with 0.05 M Tris–HCl (pH 6.8), using a linear (0.1–0.25 M) concentration gradient of NaCl. The yields were 1260 mg α-lactalbumin, 1290 mg β-lactoglobulin B and 2280 mg β-lactoglobulin A from 1 l rennet whey. 相似文献
25.
26.
Roger Scholz Falk Hoffmann Sandra von Sachsen Welf-Guntram Drossel Carsten Klöhn Christian Voigt 《Journal of biomechanics》2013
In total hip arthroplasty and particularly in revision surgery, computer assisted pre-operative prediction of the best possible anchorage strategy for implant fixation would be a great help to the surgeon. Computer simulation relies on validated numerical models. In the current study, three density–elasticity relationships (No. 1–3) from the literature for inhomogeneous material parameter assignment from CT data in automated finite element (FE) modeling of long bones were evaluated for their suitability for FE modeling of human pelvic bone. Numerical modal analysis was conducted on 10 FE models of hemipelvic bone specimens and compared to the gold standard provided by experimental modal analysis results from a previous in-vitro study on the same specimens. Overall, calculated resonance frequencies came out lower than measured values. Magnitude of mean relative deviation of numerical resonance frequencies with regard to measured values is lowest for the density–elasticity relationship No. 3 (−15.9%) and considerably higher for both density–elasticity relationships No. 1 (−41.1%) and No. 2 (−45.0%). Mean MAC values over all specimens amount to 77.8% (No. 1), 78.5% (No. 2), and 83.0% (No. 3). MAC results show, that mode shapes are only slightly influenced by material distribution. Calculated resonance frequencies are generally lower than measured values, which indicates, that numerical models lack stiffness. Even when using the best suited (No. 3) out of three investigated density–elasticity relationships, in FE modeling of pelvic bone a considerable underestimation of model stiffness has to be taken into account. 相似文献
27.
28.
29.
K. Sasikala Ch.V. Ramana P. Raghuveer Rao M. Subrahmanyam 《FEMS microbiology letters》1990,72(1-2):23-28
Abstract Photoproduction of hydrogen, nitrogenase activity (acetylene reduction) and hydrogenase activity (methylene blue dye reduction) were studied in free and alginate immobilized whole cells of a purple non-sulfur photosynthetic bacterium Rhodobacter sphaeroides O.U. 001. Four-fold increase in hydrogen production, two-fold increase in nitrogenase activity and 1.2-fold increase in the hydrogenase activity were observed in immobilized cells compared to free cells. Effect of various inhibitors (CO and C2 H2 ) and electron donor (H2 ) on the above three functions by free and immobilized cells has also been studied. 相似文献
30.
Continuum methods are not accurate enough for flows at high Knudsen numbers, whereas rigorous molecular dynamics (MD) methods are too costly for simulations at practical dimensions. Hard-sphere (HS) model is a simplified MD method efficient for dilute gaseous flow but is of poor parallelism due to its event-driven nature, which sets a strong limitation to its large-scale applications. In this work, pseudo-particle modelling, a time-driven modelling approach is coupled with HS model to construct a scalable parallel method capable of simulating flows and transport processes at high Knudsen numbers without losing necessary molecular details in describing their macro-scale behaviours. The method is validated in several classical simulation cases and its performance is evaluated to be favourable. To demonstrate the potential applications of this method, we also simulate the diffusion of small molecules in multi-scale porous media which is related to catalysis, material preparation and micro chemical engineering in the long term. 相似文献