全文获取类型
收费全文 | 962562篇 |
免费 | 104545篇 |
国内免费 | 476篇 |
专业分类
1067583篇 |
出版年
2018年 | 8514篇 |
2016年 | 11594篇 |
2015年 | 15479篇 |
2014年 | 18536篇 |
2013年 | 25950篇 |
2012年 | 29792篇 |
2011年 | 30329篇 |
2010年 | 20857篇 |
2009年 | 19272篇 |
2008年 | 27595篇 |
2007年 | 28514篇 |
2006年 | 26871篇 |
2005年 | 25703篇 |
2004年 | 25685篇 |
2003年 | 24765篇 |
2002年 | 24198篇 |
2001年 | 40794篇 |
2000年 | 41052篇 |
1999年 | 32831篇 |
1998年 | 12228篇 |
1997年 | 12670篇 |
1996年 | 12097篇 |
1995年 | 11427篇 |
1994年 | 11225篇 |
1993年 | 11041篇 |
1992年 | 27647篇 |
1991年 | 27187篇 |
1990年 | 26874篇 |
1989年 | 26174篇 |
1988年 | 24214篇 |
1987年 | 23556篇 |
1986年 | 21645篇 |
1985年 | 21945篇 |
1984年 | 18078篇 |
1983年 | 15638篇 |
1982年 | 12086篇 |
1981年 | 10749篇 |
1980年 | 10288篇 |
1979年 | 17255篇 |
1978年 | 13747篇 |
1977年 | 12468篇 |
1976年 | 11880篇 |
1975年 | 13142篇 |
1974年 | 14278篇 |
1973年 | 14035篇 |
1972年 | 12524篇 |
1971年 | 11676篇 |
1970年 | 9996篇 |
1969年 | 9466篇 |
1968年 | 8566篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
994.
995.
Antigenic change on the surface of immature oocytes of Ascaris occurred during passage through the oviduct. Using immunodiffusion and immunoelectrophoretic techniques we examined the possible relationship between the antigenic change of immature oocytes and the junctional fluid (JF) which is present in the fertilization chamber. From the immunodiffusion it was found that the anti-immature oocyte serum (A-I serum) had more immunoprecipitation arcs than did the anti-mature oocyte serum (A-M serum) when reacted against the junctional fluid. This indicated that A-I serum contained more immunoglobulins that reacted with junctional fluid than did the A-M serum. This result was substantiated by using immunoelectrophoretic analysis and two dimension crossed immunoelectrophoresis. Our results suggest that during the migration toward the oviduct-uterine junction the immature oocytes might shed surface proteins into the luminal fluid. Alternatively, the membrane surface of mature oocytes may be altered by the interaction with the substances present in the junctional fluid. 相似文献
996.
997.
998.
The ergosterol and lecithin absorption IR-spectra were studied in a nonpolar anhydrous medium. The thermodynamical and spectral characteristics of dimeric associates and the enthalpy value for trimeric associates of this sterol are determined. Thermodynamical and spectral parameters of ergosterol intermolecular associates with lecithin in a nonpolar anhydrous medium are found. It is established that the intermolecular interaction of lecithin with ergosterol occurs according to the mechanism of hydrogen bond. A conclusion is drawn that the presence of binary bonds and methyl groups in the cyclic and aliphatic parts of the sterol molecule affects greatly the structure of the model membrane and its strength. It is shown that under conditions of the experiment the oxygen of the phosphate group contributes to formation of the molecular associates of lecithin with sterols and not that of the carbonyl group. The obtained experimental data may be at use when studying structural disturbances of native membranes in norm and with different pathologies. 相似文献
999.
1000.
A total of 764 breeding soundness examinations was conducted on beef bulls utilizing the method of examination and criteria for classifying bulls of the Society for Theriogenology. In addition to this examination each bull was subjected to scrotal circumference measurement and to weighing. Classification of the bulls according to breeding soundness potentials was as follows: 88% of the bulls were satisfactory potential breeders, 8% of the bulls were questionable potential breeders and 4% of the bulls were unsatisfactory potential breeders. The proportions of bulls in each classification; satisfactory, questionable, or unsatisfactory; were not different among the four breeds evaluated. The majority of bulls evaluated in this study were between 14 and 36 months of age and weighed between 900 and 1500 pounds. For the ages and weights evaluated, scrotal circumference measurement variances were not closely related to age and weight differences. There was a tendency shown for “Questionable” and “Unsatisfactory Potential Breeders” to have smaller scrotal circumference measurements. The study indicates that Angus, Charolais, Horned Hereford and Polled Hereford bulls of breeding ages and weights should have scrotal circumference measurements of at least 32 centimeters in order to be classified as “Satisfactory Potential Breeders”. 相似文献