全文获取类型
收费全文 | 6249篇 |
免费 | 639篇 |
国内免费 | 1篇 |
出版年
2023年 | 40篇 |
2022年 | 54篇 |
2021年 | 119篇 |
2020年 | 83篇 |
2019年 | 82篇 |
2018年 | 86篇 |
2017年 | 100篇 |
2016年 | 164篇 |
2015年 | 284篇 |
2014年 | 309篇 |
2013年 | 340篇 |
2012年 | 446篇 |
2011年 | 397篇 |
2010年 | 250篇 |
2009年 | 242篇 |
2008年 | 346篇 |
2007年 | 286篇 |
2006年 | 300篇 |
2005年 | 282篇 |
2004年 | 261篇 |
2003年 | 251篇 |
2002年 | 243篇 |
2001年 | 115篇 |
2000年 | 110篇 |
1999年 | 113篇 |
1998年 | 85篇 |
1997年 | 69篇 |
1996年 | 62篇 |
1995年 | 53篇 |
1994年 | 55篇 |
1993年 | 55篇 |
1992年 | 93篇 |
1991年 | 71篇 |
1990年 | 86篇 |
1989年 | 73篇 |
1988年 | 53篇 |
1987年 | 62篇 |
1986年 | 51篇 |
1985年 | 41篇 |
1984年 | 59篇 |
1983年 | 32篇 |
1981年 | 42篇 |
1980年 | 29篇 |
1979年 | 56篇 |
1978年 | 32篇 |
1977年 | 45篇 |
1976年 | 41篇 |
1975年 | 25篇 |
1974年 | 36篇 |
1973年 | 31篇 |
排序方式: 共有6889条查询结果,搜索用时 15 毫秒
81.
Isolation of two L-asparaginases from guinea pig liver 总被引:1,自引:0,他引:1
82.
Inactivation of Aspartic Transcarbamylase in Sporulating Bacillus subtilis: Demonstration of a Requirement for Metabolic Energy 总被引:14,自引:13,他引:1 下载免费PDF全文
The aspartic transcarbamylase (ATCase) activity of Bacillus subtilis cells disappears rapidly from stationary-phase cells prior to sporulation. ATCase activity does not appear in the culture fluid during the stationary phase; hence the enzyme appears to be inactivated in the cells. The enzyme is inactivated normally in two different mutants lacking proteases; the activity is very stable in crude extracts of cells or in the culture fluid. These results suggest that ATCase is not inactivated by the general proteolysis that occurs in sporulating bacteria. The inactivation of ATCase can be completely inhibited after it has begun by oxygen starvation or addition of fluoroacetate. Inhibitors of oxidative phosphorylation and electron transport also interrupt the inactivation of ATCase. The inactivation of ATCase is very slow in two mutant strains that are deficient in enzymes of tricarboxylic acid cycle. Addition of gluconate to stationary cultures of the mutant strains, which is known to restore depleted adenosine 5'-triphosphate pools in these bacteria, also restores inactivation of ATCase. These experiments support the conclusion that the generation of metabolic energy is necessary for the inactivation of ATCase in stationary cells. ATCase activity is stable in growing cells in which ATCase synthesis is repressed by addition of uracil; the enzyme is inactivated normally, however, when such cells cease growing. 相似文献
83.
The objective of this study was to determine the feasibility of using airborne T3 coliphage as a viral tracer in microbial aerosols. Although T3 coliphage was relatively stable when stored either at temperatures ranging from 21 to 37 C or in the frozen state at -20 C, there was a 2-log loss in infectivity when stored for 72 days at 4 C. Either agitation of stored coliphage suspensions held at 31 C or wide fluctuations in storage temperature produced an increased loss of infectivity. In the airborne state, freshly prepared coliphage and stored coliphage behaved similarly, with survival diminishing as the relative humidity (RH) was lowered. The greatest loss occurred during the first five min following aerosolization. The results showed that only under certain conditions of temperature and relative humidity can T3 coliphage be used as a satisfactory aerosol tracer. 相似文献
84.
85.
Louise Taichert 《The Western journal of medicine》1968,109(4):286-290
Each professional, whether pediatrician, neurologist, psychiatrist, psychologist or teacher, in evaluating behavioral, neuromuscular, and emotional factors with the tools of his discipline, can arrive independently at very similar views regarding etiology and diagnosis of learning and language disorders. Even though this is possible, it is essential to have the many disciplines work together. This manner of sharing information is not only supportive to the patient, but to the physician as well.The pediatrician''s role does not stop, however, with the diagnosis, but continues with the working through of problems that the child and parents present to one another. 相似文献
86.
The cystine-containing peptides of horse growth hormone were isolated and their amino acid sequences determined. Four unique half-cystine residues occur in two peptides, one containing 11 and the other, at the C-terminus of the protein, 15 amino acids. These sequences are compared with published data on growth hormones from other species. 相似文献
87.
Summary In vitro,Phoma liliana could not be distinguished from the later-describedP. ehretiae and two incidental isolates fromMangifera andChrysanthemum. Starting from the principle of the classification in the Deuteromycetes, our conclusion is that we must speak of one and the same form-species, which can be found on different plants. 相似文献
88.
Polyuronic acids produced by Pseudomonas aeruginosa 总被引:14,自引:0,他引:14
89.
Titration and Neutralization of Poliovirus in Micro Tissue Culture Under Increased Carbon Dioxide 总被引:5,自引:3,他引:2 下载免费PDF全文
Modification of the micro tissue culture technique, including incubation under increased CO(2), resulted in prolongation of the viability of the cells. As a consequence, satisfactory titrations of poliovirus and of poliovirus antiserum have been achieved by the micro method. The technique offers a number of advantages over conventional methods. 相似文献
90.
Ted C. J. Turlings James H. Tumlinson W. Joe Lewis Louise E. M. Vet 《Journal of Insect Behavior》1989,2(2):217-225
Females of Cotesia marginiventris(Cresson), a generalist larval parasitoid, were observed to respond to host related odors in a four-arm olfactometer. The females were significantly more responsive to the odors after a brief contact experience with host-damaged leaves contaminated with host by products. During the experience, actual encounters with hosts were not required to improve subsequent responses to host-related odors. The response to odors of the plant-host complex with which parasitoids had experience was significantly higher than the response to odors of an alternative plant-host complex. This suggests that the experience effect is due, at least partly, to associative learning. We suspect that females of this generalist parasitoid, as was recently found for those of a specialist, recognize specific semiochemicals when they contact frass of suitable host larvae. The parasitoids, subsequently, associate the surrounding odors with the possible presence of hosts, and use these odors as cues in their search for more hosts. This could be an important component in the host-searching behavior of many parasitoids.Mention of a proprietary product does not constitute an endorsement or the recommendation for its use by the USDA. 相似文献