全文获取类型
收费全文 | 19483篇 |
免费 | 1823篇 |
国内免费 | 6575篇 |
出版年
2023年 | 551篇 |
2022年 | 617篇 |
2021年 | 864篇 |
2020年 | 972篇 |
2019年 | 1142篇 |
2018年 | 1046篇 |
2017年 | 974篇 |
2016年 | 982篇 |
2015年 | 1023篇 |
2014年 | 1167篇 |
2013年 | 1716篇 |
2012年 | 1030篇 |
2011年 | 1088篇 |
2010年 | 868篇 |
2009年 | 1129篇 |
2008年 | 1040篇 |
2007年 | 1149篇 |
2006年 | 1059篇 |
2005年 | 927篇 |
2004年 | 835篇 |
2003年 | 813篇 |
2002年 | 692篇 |
2001年 | 564篇 |
2000年 | 515篇 |
1999年 | 481篇 |
1998年 | 402篇 |
1997年 | 369篇 |
1996年 | 342篇 |
1995年 | 356篇 |
1994年 | 363篇 |
1993年 | 312篇 |
1992年 | 274篇 |
1991年 | 225篇 |
1990年 | 212篇 |
1989年 | 231篇 |
1988年 | 169篇 |
1987年 | 141篇 |
1986年 | 121篇 |
1985年 | 157篇 |
1984年 | 191篇 |
1983年 | 115篇 |
1982年 | 162篇 |
1981年 | 93篇 |
1980年 | 85篇 |
1979年 | 85篇 |
1978年 | 48篇 |
1977年 | 29篇 |
1976年 | 39篇 |
1974年 | 30篇 |
1973年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
12.
Hitoshi Sawada Hideyoshi Yokosawa Shin-Ichi Ishii Motonori Hoshi 《Molecular reproduction and development》1982,5(3):291-301
The presence of a protease has been demonstrated in sperm of the solitary ascidian, Halocynthia roretzi, by using t-butyloxycarbonyl-L-Val-L-Pro-L-Arg-4-methylcoumaryl-7-amide (Boc-Val-Pro-Arg-MCA) and other arginyl or lysyl MCA derivatives as substrates. Several properties of the enzyme were investigated in a crude extract. The activity had a pH optimum near 8.0 and was enhanced by the addition of CaCl2. The Km value of 87μM was determined for Boc-Val-Pro-Arg-MCA under the optimal conditions. An apparent molecular weight was estimated to be 35,000 by gel filtration. The enzyme was inhibited with diisopropyl fluorophosphate, leupeptin, antipain, p-aminobenzamidine, Val-Pro-Arg-CH2Cl, and soybean trypsin inhibitor, but scarcely inhibited with chymostatin, elastatinal, p-chloromercuribenzoic acid, tosyl-Lys-CH2Cl, and tosyl-Phe-CH2Cl. Boc-Val-Pro-Arg-MCA, the most susceptible of the substrates examined, showed the most effective inhibition against fertilization of ascidian eggs. Thus, this enzyme in ascidian sperm extract has features closely similar to mammalian acrosin [EC 3.4.21.10], and we conclude that the enzyme is involved in fertilization as one of the lysins. 相似文献
13.
14.
15.
16.
Jerry W. McClure 《Phytochemistry》1974,13(7):1065-1069
Five-day-old etiolated barley shoots respond to brief illumination with red light by increasing their level of PAL ca 50% within 5 hr. When assayed s 相似文献
17.
18.
19.
20.
L.E. Palma-Cano H.A. Piñon-Castillo S.H. Tarango-Rivero A. Carbon J. Salas-Leiva L.N. Muñoz-Castellanos C. Cravo-Laureau R. Duran E. Orrantia-Borunda 《Letters in applied microbiology》2021,72(5):556-569
We described the bacterial diversity of walnut grove soils under organic and conventional farming. The bacterial communities of rhizospheric and nonrhizospheric soils of pecan tree (Carya illinoensis K. Koch) were compared considering two phenological stages (sprouting and ripening). Sixteen operational taxonomic units (OTUs) were identified significantly more abundant according to the plant development, only one according to the farming condition, and none according to the soil origin. The OTUs specificaly abundant according to plant development included Actinobateria (2) and Betaproteobacteria (1) related OTUs more abundant at the sprouting stage, while at the fruit ripening (FR) stage the more abundant OTUs were related to Actinobacteria (6), Alphaproteobacteria (6), and unclassified Bacteria (1). The Gaiellaceae OTU18 (Actinobacteria) was more abundant under conventional farming. Thus, our study revealed that the plant development stage was the main factor shaping the bacterial community structure, while less influence was noticed for the farming condition. The bacterial communities exhibited specific metabolic capacities, a large range of carbon sources being used at the FR stage. The identified OTUs specifically more abundant represent indicators providing useful information on soil condition, potential tools for the management of soil bacterial communities. 相似文献