全文获取类型
收费全文 | 5208篇 |
免费 | 390篇 |
国内免费 | 478篇 |
出版年
2024年 | 6篇 |
2023年 | 60篇 |
2022年 | 171篇 |
2021年 | 308篇 |
2020年 | 205篇 |
2019年 | 229篇 |
2018年 | 250篇 |
2017年 | 179篇 |
2016年 | 232篇 |
2015年 | 314篇 |
2014年 | 390篇 |
2013年 | 393篇 |
2012年 | 482篇 |
2011年 | 429篇 |
2010年 | 276篇 |
2009年 | 264篇 |
2008年 | 278篇 |
2007年 | 252篇 |
2006年 | 194篇 |
2005年 | 146篇 |
2004年 | 161篇 |
2003年 | 134篇 |
2002年 | 93篇 |
2001年 | 76篇 |
2000年 | 79篇 |
1999年 | 73篇 |
1998年 | 43篇 |
1997年 | 46篇 |
1996年 | 46篇 |
1995年 | 40篇 |
1994年 | 29篇 |
1993年 | 27篇 |
1992年 | 26篇 |
1991年 | 17篇 |
1990年 | 17篇 |
1989年 | 20篇 |
1988年 | 8篇 |
1987年 | 9篇 |
1986年 | 10篇 |
1985年 | 10篇 |
1984年 | 6篇 |
1983年 | 3篇 |
1979年 | 8篇 |
1975年 | 7篇 |
1974年 | 4篇 |
1971年 | 4篇 |
1970年 | 4篇 |
1969年 | 2篇 |
1966年 | 3篇 |
1965年 | 3篇 |
排序方式: 共有6076条查询结果,搜索用时 15 毫秒
11.
This paper deals with the role of light in the germination of akinetes of Anabaena azollae. The two maxima action spectra are situated at 385 and 615 nm and the stimulation of the germination process by photosynthate was confirmed. The photoreceptor absorbing at 385 nm was identified as a flavin and that at 615 nm as a phytochrome. A model is suggested for the mode of action of light in the germination of akinetes of blue-green algae.C. Tsui 相似文献
12.
13.
根癌农杆菌Ti质粒的T区DNA带有致瘤基因,其基因1和基因2编码生长素吲哚乙酸生物合成途径中的两个酶。以pGV 354(pBR322质粒中插有Ti质粒C 58 T区DNA的HindⅢ15—HindⅢ22大片段)重组质粒出发,我们分离了基因1和基因2,并构建了带有卡那霉素抗性基因的重组质粒pBZ 692,通过基因载体pGV 3850,我们将基因1和基因2引入了高等植物。结果证明基因1和基因2能促使烟草、向日葵、土豆等转化组织分化长根,转化的根在MS_0培养基上能脱分化形成愈伤组织并自主生长,在转化的组织中有转化标记胭脂碱的存在。 相似文献
14.
Masahiro Miyazaki Yasunori Suzuki Munehiro Oda Akira Kawai Liyan Bai Jiro Sato 《In vitro cellular & developmental biology. Plant》1989,25(9):839-848
Summary For serum-free primary culture of adult rat hepatocytes, a synthetic medium DM-160 and rat-tail collagen were selected for
the basal medium and for the culture substratum, respectively. Barbiturates, such as phenobarbital and 1-ethyl-5-isobutylbarbiturate,
efficiently supported survival of hepatocytes and maintained their morphologic features at lower concentrations under the
serum-free conditions than under the serum-supplemented conditions. However, the hepatocyte survival rates under the serum-free
conditions were lower than those under the serum-supplemented conditions in the presence or absence of barbiturates. Supplementation
of the basal medium with a combination of five groups of factors (5Fs), such as eight amino acids (Ala, Arg, Gly, Ile, Met,
Phe, Pro, and Trp), two unsaturated fatty acids (linoleate and oleate), a protease inhibitor (aprotinin), three vitamins (A,
C, and E), and five trace elements (Mn, Fe, Cu, Zn, and Se), improved the hepatocyte survival under the serum-free conditions
in the presence or absence of barbiturates. In other words, the serum could be completely substituted by the 5Fs. Hepatocyte
cultures maintained in the 5Fs-suppelemented basal medium showed excellent induction of tyrosine aminotransferase activity
in response to dexamethasone in the presence or absence of barbiturates. The efficiency of the 5Fs-supplemented basal medium
for maintaining hepatocytes was not inferior to those of other media in common use with hepatocytes, such as Williams' medium
E and Waymouth's medium MB-752/1. In conclusion, maintenance of functional hepatocytes in serum-free primary culture could
be improved by use of the new medium preparation (the 5Fs-supplemented DM-160) in the presence of barbiturates.
This work was supported by a grant no. 61771923 from the Ministry of Education, Science and Culture of Japan. 相似文献
15.
稀土元素对甜菜种子萌发,幼苗生长及块根产量的影响 总被引:4,自引:0,他引:4
本文研究了稀土元素对甜菜的生物效应。结果表明,稀土元素可显著地提高种子萌发率,促进幼苗生长,增加幼苗根系活力、叶片净光合速率与块根产量,并明显地降低了甜菜叶片细胞膜在低温下的透性,即提高了叶片的抗寒力。 相似文献
16.
利用强阳离子交换柱从Saponaria officinalis L种子中分离出一种肥皂草素(Saporin)成分。它在无细胞体系中显示了较强的抑制蛋白合成的活性,与抗体连接后能特异性杀伤靶细胞。 相似文献
17.
Kaposi's sarcoma-associated herpesvirus contains G protein-coupled receptor and cyclin D homologs which are expressed in Kaposi's sarcoma and malignant lymphoma. 总被引:21,自引:11,他引:10 下载免费PDF全文
E Cesarman R G Nador F Bai R A Bohenzky J J Russo P S Moore Y Chang D M Knowles 《Journal of virology》1996,70(11):8218-8223
A new human herpesvirus was recently identified in all forms of Kaposi's sarcoma (Kaposi's sarcoma-associated herpesvirus [KSHV] or human herpesvirus 8), as well as in primary effusion (body cavity-based) lymphomas (PELs). A 12.3-kb-long KSHV clone was obtained from a PEL genomic library. Sequencing of this clone revealed extensive homology and colinearity with the right end of the herpesvirus saimiri (HVS) genome and more limited homology to the left end of the Epstein-Barr virus genome. Four open reading frames (ORFs) were sequenced and characterized; these are homologous to the following viral and/or cellular genes: (i) Epstein-Barr virus membrane antigen p140 and HVS p160, (ii) HVS and cellular type D cyclins, (iii) HVS and cellular G protein-coupled receptors, and (iv) HVS. Since there is considerable evidence that cyclin D1 and some G protein-coupled receptors contribute to the development of specific cancers, the presence of KSHV homologs of these genes provides support for a role for KSHV in malignant transformation. All ORFs identified are transcribed in PELs and Kaposi's sarcoma tissues, further suggesting an active role for KSHV in these diseases. 相似文献
18.
酿酒酵母属(S. cereviae)变异株和粟酒裂殖酵母属(S. pombe)变异株进行属间原生质体融合得到融合株SPSC,该融合株比S. cereviae具有强的自身絮凝能力。以葡萄糖浓度150g/L的底物在30~44℃的温度范围内进行摇瓶厌氧发酵,获得最佳温度范围为34~38℃,最高发酵温度为40℃。在有效容积2.35L悬浮床反应器中,在pH值3.0~5.0范围内进行连续发酵,获得最适发酵pH为3.5~4.5。 相似文献
19.
无花果蛋白酶通过8%戊二醛活化载体,共价结合到聚苯乙烯阴离子交换树脂GM201上,固定化作用在pH7.7,酶浓度0.8mg/g树脂,4℃下进行6h。得到的固定化酶表观K_m值(酪蛋白,1.11×10~(-4)mol/L)小于溶液酶K_m值(1.96×10~(-4)mol/L);固定化酶活性在pH6~8保持稳定,溶液酶最适pH为7.2;固定化酶最适温度由溶液酶的50~60℃移至37℃;固定化酶25℃保持7d,重复水解酪蛋白7次后,保留83.3%活性。固定化酶对酪蛋白水解度达47.5%,对大豆球蛋白达11.6%。 相似文献
20.
利用KCN、H_2O2和SDS的选择性反应引起的SOD同工酶谱带变化即可鉴别粗抽提液中的SOD同工酶类型;用这种方法对五株不同种根霉的鉴别实验表明,它们均不同程度地含有Cu,Zn型和Mn型两种SOD,前者约占80%左右,后者只占20%左右。用邻苯三酚自氧化法对样品中SOD活性测定结果与在同工酶谱上的鉴别结果基本一致。 相似文献