全文获取类型
收费全文 | 42498篇 |
免费 | 3026篇 |
国内免费 | 5711篇 |
出版年
2024年 | 189篇 |
2023年 | 913篇 |
2022年 | 1146篇 |
2021年 | 1410篇 |
2020年 | 1423篇 |
2019年 | 2004篇 |
2018年 | 1612篇 |
2017年 | 1450篇 |
2016年 | 1368篇 |
2015年 | 1323篇 |
2014年 | 2138篇 |
2013年 | 3086篇 |
2012年 | 1715篇 |
2011年 | 2015篇 |
2010年 | 1549篇 |
2009年 | 2022篇 |
2008年 | 1991篇 |
2007年 | 2186篇 |
2006年 | 1930篇 |
2005年 | 1761篇 |
2004年 | 1563篇 |
2003年 | 1417篇 |
2002年 | 1286篇 |
2001年 | 1015篇 |
2000年 | 898篇 |
1999年 | 821篇 |
1998年 | 802篇 |
1997年 | 703篇 |
1996年 | 598篇 |
1995年 | 570篇 |
1994年 | 546篇 |
1993年 | 498篇 |
1992年 | 487篇 |
1991年 | 466篇 |
1990年 | 355篇 |
1989年 | 347篇 |
1988年 | 354篇 |
1987年 | 282篇 |
1986年 | 316篇 |
1985年 | 541篇 |
1984年 | 637篇 |
1983年 | 351篇 |
1982年 | 510篇 |
1981年 | 496篇 |
1980年 | 428篇 |
1979年 | 332篇 |
1978年 | 241篇 |
1977年 | 253篇 |
1976年 | 217篇 |
1973年 | 188篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
121.
122.
123.
For flexible peptides, nuclear Overhauser Effects (NOE) experiments do not provide enough information to ensure a correct definition of their solution structure. The use of distance constraints, derived from the knowledge of proton chemical shifts, is developed to restrict the number of possible conformations. In the case of flexible molecules, randomization appears as an important factor of the correct estimation of the chemical shifts from the 3D structure. The refinement of the solution structure of the highly flexible AVP-like parallel dimer is described to illustrate this process. 相似文献
124.
Prof. D. S. Bhoj 《Biometrical journal. Biometrische Zeitschrift》1987,29(5):589-594
A statistic is proposed for testing the hypothesis of equality of the means of a bivariate normal distribution with unknown common variance and correlation coefficient when observations are missing on one of the variates. Expressions for the second and fourth central moments of the statistic are obtained. These moments are used to approximate the distribution of the statistic by a Student's t distribution under the null hypothesis. The powers of the test are computed and compared with those of the conventional paired t and the other known statistics. 相似文献
125.
Dinesh S. Bhoj 《Biometrical journal. Biometrische Zeitschrift》1989,31(3):279-288
Two statistics are proposed for testing the hypothesis of equality of the means of a bivariate normal distribution with unknown common variance and correlation coefficient when observations are missing on both variates. One of the statistics reduces to the one proposed by Bhoj (1978, 1984) when the unpaired observations on the variates are equal. The distributions of the statistics are approximated by well known distributions under the null hypothesis. The empirical powers of the tests are computed and compared with those of some known statistics. The comparison supports the use of one of the statistics proposed in this paper. 相似文献
126.
Dennis T. Villareal Caroline M. Apovian Robert F. Kushner Samuel Klein 《Obesity (Silver Spring, Md.)》2005,13(11):1849-1863
Obesity causes serious medical complications and impairs quality of life. Moreover, in older persons, obesity can exacerbate the age‐related decline in physical function and lead to frailty. However, appropriate treatment for obesity in older persons is controversial because of the reduction in relative health risks associated with increasing body mass index and the concern that weight loss could have potential harmful effects in the older population. This joint position statement from the American Society for Nutrition and NAASO, The Obesity Society reviews the clinical issues related to obesity in older persons and provides health professionals with appropriate weight‐management guidelines for obese older patients. The current data show that weight‐loss therapy improves physical function, quality of life, and the medical complications associated with obesity in older persons. Therefore, weight‐loss therapy that minimizes muscle and bone losses is recommended for older persons who are obese and who have functional impairments or medical complications that can benefit from weight loss. 相似文献
127.
A number of methods of construction of partially balanced incomplete block designs with nested rows and columns are developed and new balanced incomplete block designs with nested rows and columns are obtained as a by-product. 相似文献
128.
Michael Brenowitz Celia Bonaventura Joseph Bonaventura Elisabetta Gianazza 《Archives of biochemistry and biophysics》1981,210(2):748-761
The hemocyanin of Limulus polyphemus is a 48-subunit aggregate. This 3.3 × 106-dalton oligomer is composed of structurally and functionally heterogeneous subunits. Using polyacrylamide electrophoresis J. Markl, A. Markl, W. Schartau, and B. Linzen (J. Comp. Physiol. Ser. B130,283–292, 1979) observed 12 bands; while using immunoelectrophoresis, M. Hoylaerts, G. Preaux, R. Witters, and R. Lontie (Arch. Int. Physiol. Biochem.87, 417–418, 1979) and J. Lamy, J. Lamy, J. Weill, J. Bonaventura, C. Bonaventura, and M. Brenowitz. (Arch. Biochem. Biophys.196, 324–339, 1979) observed 8 subunits. To proceed with an analysis of subunit roles in assembly it is first necessary to determine the number of distinct subunits. Refinement of the chromatographic separation procedures has led to the isolation of 8 immunologically distinct subunits as well as additional charge isomers which cannot be distinguished immunologically. Alkaline electrophoresis revealed 15 bands and isoelectric focusing up to 17. On the basis of extensive control experiments, including composit acrylamide-agarose immunoelectrophoresis and checks for conformational isomers, aggregation, proteolysis, and other types of degradation, we conclude that the electrophoretic heterogeneity of immunologically identical subunits is not artifactual. We have extended the nomenclature used by Lamy et al. (1979) to include the electrophoretic heterogeneity by using primes (′) to denote electrophoretically distinguishable subunits which are immunologically identical. A number of patterns have become apparent by correlating the results obtained by the different techniques. For example, immunologically pure subunit II, which shows 3 bands on alkaline electrophoresis, is in fact a mixture of electrophoretically distinct subunits II, II′, II″. Except for subunits II, II′, and II″ immunoelectrophoretically identical subunits are typically homogeneous on sodium dodecyl sulfate-gels. However, slight differences in the apparent molecular weight are observed on high-resolution gels between immunologically unrelated subunits. The immunological identity and electrophoretic differences suggest that the charge isomers which are immunologically identical have similar antigenic surfaces. If a charge substitution is not in a critical location, we would expect the electrophoretically distinct but immunologically identical subunits to have identical assembly roles. Comparison of the results for Limulus hemocyanin with the hemocyanin of related species Eurypelma californicum and Androctanus australis, which have 7 and 8 immunologically distinct subunits, respectively, suggests that the calcium-mediated aggregation from 24 to 48 subunits of Limulus does not require more extensive subunit complexity. 相似文献
129.
Caroline S. Page Franz M. Matschinsky Paule E. Lacy Susan Conant 《Biochimica et Biophysica Acta (BBA)/General Subjects》1977,497(2):408-414
Electrophysiological studies of cultured rat pancreatic β-cells using intracellular microelectrodes show that exogenous insulin over the range of 0.1–10.0 μg/ml inhibits the electrical activity due to 27.8 mM glucose in a dose-related manner. This inhibitory effect is manifested by a mean increase of the membrane potential from about ?20 to ?30 mV and inhibition of the manner of cells impaled showing spike activity from 60 to less than 10%. The inhibitory influence of insulin is rapid occuring within 5 min for the highest level used. The results provide evidence for a negative feedback role of insulin in regulating its own release. 相似文献
130.
K. Kortmulder 《Acta biotheoretica》1987,36(4):275-280
The potential and realized impact of Bohm's views on biology are briefly discussed. 相似文献