全文获取类型
收费全文 | 497063篇 |
免费 | 59154篇 |
国内免费 | 231篇 |
专业分类
556448篇 |
出版年
2018年 | 4583篇 |
2017年 | 4430篇 |
2016年 | 5970篇 |
2015年 | 8019篇 |
2014年 | 9375篇 |
2013年 | 13469篇 |
2012年 | 14914篇 |
2011年 | 15316篇 |
2010年 | 10535篇 |
2009年 | 9621篇 |
2008年 | 13574篇 |
2007年 | 13929篇 |
2006年 | 13002篇 |
2005年 | 12532篇 |
2004年 | 12164篇 |
2003年 | 11986篇 |
2002年 | 11533篇 |
2001年 | 23142篇 |
2000年 | 23119篇 |
1999年 | 18211篇 |
1998年 | 6324篇 |
1997年 | 6861篇 |
1996年 | 6489篇 |
1995年 | 6026篇 |
1994年 | 5928篇 |
1993年 | 6058篇 |
1992年 | 15296篇 |
1991年 | 15166篇 |
1990年 | 14572篇 |
1989年 | 14173篇 |
1988年 | 12984篇 |
1987年 | 12528篇 |
1986年 | 11725篇 |
1985年 | 11650篇 |
1984年 | 9736篇 |
1983年 | 8393篇 |
1982年 | 6429篇 |
1981年 | 5770篇 |
1980年 | 5502篇 |
1979年 | 9207篇 |
1978年 | 7340篇 |
1977年 | 6662篇 |
1976年 | 6292篇 |
1975年 | 7010篇 |
1974年 | 7283篇 |
1973年 | 7277篇 |
1972年 | 6561篇 |
1971年 | 5997篇 |
1970年 | 5070篇 |
1969年 | 4950篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
R A Harkness G M McCreanor J Allsop D H Snow R C Harris P O Rossdale J C Ousey 《Comparative biochemistry and physiology. B, Comparative biochemistry》1990,97(3):591-596
1. Plasma hypoxanthine and xanthine concentrations are very low in the horse and low in rat, mouse and greyhound compared to concentrations in beagles, man, sheep and rabbit. 2. Activities in erythrocytes of the main enzyme metabolizing hypoxanthine, hypoxanthine phosphori-bosyltransferase, show a similar pattern (Tax et al., 1976, Comp. Biochem. Physiol. 54B, 209-212); thus low activities have been found where plasma concentrations were low. 3. Hypoxanthine phosphoribosyltransferase activities in horse tissue other than erythrocytes are similar to those in man and rabbit with high activities in brain; this enzyme may therefore be functionally important in equine brain. 相似文献
952.
Equations for the motion of an individual dust grain in the double layer of a negatively charged cylindrical probe in a glow discharge plasma are derived and solved numerically. The distribution of the electric potential near the probe is determined, and the grain charge is calculated as a function of the distance from the probe for different probe potentials. The trajectories of grains with different initial energies are traced. An analysis of the grain trajectories shows that, at a certain distance from the probe, high-energy grains may be recharged; i.e., the grain charge may change sign. The grains are found to have no direct effect on the probe current in a dusty plasma of a glow discharge. 相似文献
953.
L. I. Sapunova A. G. Lobanok I. O. Kazakevich E. A. Shlyakhotko A. N. Evtushenkov 《Applied Biochemistry and Microbiology》2006,42(3):246-251
The characteristics of xylose isomerase biosynthesis in the bacteria Arthrobacter nicotianae BIM B-5, Erwinia carotovora subsp atroseptica jn42xylA, and Escherichia coli HB101xylA have been studied. The bacteria produced the enzyme constitutively. Out of the carbon sources studied, D-glucose and D-xylose were most favorable for the biosynthesis of xylose isomerase in E. carotovora subsp. atroseptica, but the least appropriate in terms of the enzyme production efficiency in E. coli. Minimum and maximum levels of xylose isomerase formation in A. nicotianae were noted, respectively, during D-xylose and sucrose utilization. An addition to the D-xylose-containing nutrient medium of 0.1–1.5% D-glucose did not affect the enzyme synthesis in A. nicotianae, but suppressed it in Erwinia carotovora subsp. atroseptica (by 7% at the highest concentration) and Escherichia coli (by 63 and 75% at concentrations of 0.1 and 1.0%, respectively). The enzyme proteins produced by the bacteria exhibited the same substrate specificity and electrophoretic mobility (PAGE) as xylose isomerase A. nicotianae, although insignificant differences in the major physicochemical properties were noted. 相似文献
954.
955.
Dry Heat Inactivation of Bacillus subtilis var. niger Spores as a Function of Relative Humidity 总被引:2,自引:2,他引:0 下载免费PDF全文
Dry heat sterilization of Bacillus subtilis var. niger spores at 105 C is enhanced in the relative humidity range 0.03 to 0.2%. D-values of 115 and 125 C are predicted by a kinetic model with parameters set from 105 C data. These predictions are compared to observations. 相似文献
956.
The differentiation of spermatids in the marmoset (Callithrix jacchus, n = 9) testis is described here at the light-microscopic level employing serial semithin sections. The definition of 8 different phases of spermiogenesis, i.e. the formation of spermatids, is based upon the changes in the development of nucleus, acrosome and flagellum. 相似文献
957.
958.
959.
960.
George O. Poinar Jr. 《Systematic parasitology》1981,2(4):261-266
Summary A new mermithid nematode, Thaumamermis cosgrovei n. gen., n. sp. (Mermithidae: Nematoda) was found parasitizing two terrestrial isopods (Isopoda: Oniscoidea) in California. The hosts, Armadillidium vulgare (Latr.) (a pillbug) and Porcellio scaber (Latr.) (a sowbug) represent the first cases of isopods attacked by mermithid nematodes. The genus Thaumamermis can be distinguished from all previously described mermithids by the extremely dimorphic spicules, one being short and broad and the other long and filiform. It has been discovered that the nematodes are infected with an iridiovirus which commonly destroys the isopod hosts. ac]19800917 相似文献