全文获取类型
收费全文 | 28875篇 |
免费 | 2417篇 |
国内免费 | 2536篇 |
出版年
2024年 | 22篇 |
2023年 | 212篇 |
2022年 | 321篇 |
2021年 | 972篇 |
2020年 | 837篇 |
2019年 | 1010篇 |
2018年 | 1025篇 |
2017年 | 858篇 |
2016年 | 1105篇 |
2015年 | 1662篇 |
2014年 | 2084篇 |
2013年 | 2253篇 |
2012年 | 2738篇 |
2011年 | 2582篇 |
2010年 | 1686篇 |
2009年 | 1518篇 |
2008年 | 2022篇 |
2007年 | 1716篇 |
2006年 | 1552篇 |
2005年 | 1315篇 |
2004年 | 1289篇 |
2003年 | 1223篇 |
2002年 | 1074篇 |
2001年 | 516篇 |
2000年 | 392篇 |
1999年 | 319篇 |
1998年 | 267篇 |
1997年 | 169篇 |
1996年 | 162篇 |
1995年 | 153篇 |
1994年 | 115篇 |
1993年 | 98篇 |
1992年 | 97篇 |
1991年 | 74篇 |
1990年 | 45篇 |
1989年 | 64篇 |
1988年 | 38篇 |
1987年 | 34篇 |
1986年 | 32篇 |
1985年 | 30篇 |
1984年 | 12篇 |
1983年 | 11篇 |
1982年 | 20篇 |
1981年 | 7篇 |
1979年 | 7篇 |
1977年 | 7篇 |
1976年 | 6篇 |
1971年 | 5篇 |
1967年 | 6篇 |
1965年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
81.
可育的抗除草剂溴苯腈转基因小麦 总被引:21,自引:0,他引:21
报道了采用微粒轰击(Microprojectile bom bardm ent) 幼胚将除草剂抗性基因导入小麦(Triticumaestivum L.)的转化研究。实验共使用了13 个小麦品种, 从开花后14~18 d 的籽粒中剥取幼胚, 植物表达质粒含有CaMV 35S启动子控制的除草剂溴苯腈抗性基因bxn 以及筛选标记基因NTPⅡ。采用高压放电基因枪,用质粒DNA 包被的钨粒轰击预培养3 d 的幼胚。在含有卡那霉素类似物geneticin G418sulphate 的MS培养基上, 经过多步骤筛选和分化, 从800 多个幼胚中获得了16 株转化苗。除草剂抗性鉴定和Southern 杂交分析证明, 其中4 株为转基因植物,具有溴苯腈抗性, 并且自交可育。转化工作从分离幼胚到转化苗鉴定完毕, 最短时间为6 个月, 因此, 该方法是一项快速有效的基因导入技术 相似文献
82.
Li-Xin Zhang Hou-Guo Liang Jun Wang Wen-Rui Li Tian-Zhi Yu 《Photosynthesis research》1996,48(3):379-384
The 33 kDa protein of Photosystem II has one intrachain disulfide bond. Fluorescence spectroscopy shows that the major groups in the protein that bind to Ca2+ should be the carboxylic side groups of glutamic acid and/or aspartic acid. Fluorescence and Fourier-transform infrared (FTIR) spectroscopic studies indicate that the conformation of the 33 kDa protein is altered upon reduction, while the reduced protein still retains the secondary structure. FTIR spectroscopy also shows that the metal ions induce a relative decrease of unordered structure and -sheet, and a substantial increase of -helix in both the intact and the reduced 33 kDa protein. This indicates that the addition of cations results in a much more compact structure and that both the intact and the reduced 33 kDa proteins have the ability to bind calcium. The above results may suggest that the disulfide bridge is not essential for calcium binding.Abbreviations CD
circular dichroism
- FTIR
Fourier transform infrared
- La
lanthanum
- PS
photosystem
- Tb
terbium 相似文献
83.
Chae Oh Lim Soo In Lee Woo Sik Chung Sung Han Park Inhwan Hwang Moo Je Cho 《Plant molecular biology》1996,30(2):373-379
A cDNA encoding a new phytocystatin isotype named BCPI-1 was isolated from a cDNA library of Chinese cabbage flower buds. The BCPI-1 clone encodes 199 amino acids resulting in a protein much larger than other known phytocystatins. BCPI-1 has an unusually long C-terminus. A BCPI-1 fusion protein expressed in Escherichia coli strongly inhibits the enzymatic activity of papain, a cysteine proteinase. Genomic Southern blot analysis revealed that the BCPI gene is a member of a small multi-gene family in Chinese cabbage. Northern blot analysis showed that it is differentially expressed in the flower bud, leaf and root. 相似文献
84.
Purification and characterization of a fibrinolytic enzyme produced from Bacillus sp. strain CK 11-4 screened from Chungkook-Jang. 总被引:13,自引:0,他引:13 下载免费PDF全文
Bacillus sp. strain CK 11-4, which produces a strongly fibrinolytic enzyme, was screened from Chungkook-Jang, a traditional Korean fermented-soybean sauce. The fibrinolytic enzyme (CK) was purified from supernatant of Bacillus sp. strain CK 11-4 culture broth and showed thermophilic, hydrophilic, and strong fibrinolytic activity. The optimum temperature and pH were 70 degrees C and 10.5, respectively, and the molecular weight was 28,200 as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The first 14 amino acids of the N-terminal sequence of CK are Ala-Gin-Thr-Val-Pro-Tyr-Gly-Ile-Pro-Leu-Ile-Lys-Ala-Asp. This sequence is identical to that of subtilisin Carlsberg and different from that of nattokinase, but CK showed a level of fibrinolytic activity that was about eight times higher than that of subtilisin Carlsberg. The amidolytic activity of CK increased about twofold at the initial state of the reaction when CK enzyme was added to a mixture of plasminogen and substrate (H-D-Val-Leu-Lys-pNA). A similar result was also obtained from fibrin plate analysis. 相似文献
85.
Extractive lactic acid fermentation in poly (ethyleneimine)-based aqueous two-phase system 总被引:3,自引:0,他引:3
The potential of an aqueous two-phase system composed of a polycation, poly(ethyleneimine) (PEI), and an uncharged polymer, (hydroxyethyl) cellulose (HEC), for extractive lactic acid fermentation was tested. Batch fermentation with 20 g/L glucose in two-phase medium using Lactococcus lactis without external pH control resulted in 3-4 times higher amount of lactate and biomass produced as compared to that in a conventional one-phase medium. Lactic acid was preferentially partitioned to the PEI-rich bottom phase. However, the cells which favored the HEC-rich top phase in a fresh two-phase medium were partitioned to a significant extent to the bottom phase after fermentation. Addition of phosphate buffer or pH adjustment to 6.5 after fermentation caused fewer cells to move to the bottom phase. With external pH control, fermentation in normal and two-phase medium showed no marked differences in glucose consumption and lactic acid yield, except that about 1.3 times higher cell density was obtained in the two-phase broth, especially at initial glucose concentrations of 50-100 g/L. Use of higher concentration of phosphate during batch fermentation in the two-phase medium with 50 g/L sugar provided a 15% higher yield of lactic acid, but the growth rate of cells was nearly half of the normal, thus affecting the productivity. Continuous fermentation with twice the normal phosphate concentration resulted in higher cell density, product yield, and productivity in two-phase medium than in monophasic medium. (c) 1996 John Wiley & Sons, Inc. 相似文献
86.
Shuji Nakamura David W. Stock Karen L. Wydner Jacques A. Bollekens Kenichi Takeshita Brian M. Nagai Shigeru Chiba Toshio Kitamura Thomas M. Freeland Zhiyong Zhao Jun Minowada Jeanne B. Lawrence Kenneth M. Weiss Frank H. Ruddle 《Genomics》1996,38(3):314
We have cloned a new Dlx gene (Dlx7) from human and mouse that may represent the mammalian orthologue of the newt geneNvHBox-5.The homeodomains of these genes are highly similar to all other vertebrate Dlx genes, and regions of similarity also exist between mammalian Dlx7 and a subset of vertebrate Dlx genes downstream of the homeodomain. The sequence divergence between human and mouse Dlx7 in these regions is greater than that predicted from comparisons of other vertebrate Dlx genes, however, and there is little sequence similarity upstream of the homeodomain both between these two genes and with other Dlx genes. We present evidence for alternative splicing of mouseDlx7upstream of the homeodomain that may account for some of this divergence. We have mapped humanDLX7distal to the 5′ end of the HOXB cluster at an estimated distance of between 1 and 2 Mb by FISH. Both the human and the mouse Dlx7 are shown to be closely linked to Dlx3 in a convergently transcribed orientation. These mapping results support the possibility that vertebrate distal-less genes have been duplicated in concert with the Hox clusters. 相似文献
87.
Kazutoyo Osoegawa Rie Susukida Saishi Okano Jun Kudoh Shinsei Minoshima Nobuyoshi Shimizu Pieter J. de Jong Juergen Groet Jane Ives Hans Lehrach Dean Nizetic Eiichi Soeda 《Genomics》1996,32(3):375
The major phenotypic features of Down syndrome have been correlated with partial trisomies of chromosome 21, allowing us to define the candidate gene region to a 4-Mb segment on the 21q22.2 band. We present here a high-resolution physical map with megabase-sized cosmid/PAC contigs. This ordered clone library has provided unique material for the integration of a variety of mappable objects, including exons, cDNAs, restriction sites, etc. Furthermore, our results have exemplified a strategy for the completion of the chromosome 21 map to sequencing. 相似文献
88.
89.
人分裂细胞核抗原基因片段的筛选、测序及对启动子的分析 总被引:1,自引:0,他引:1
经6.6×105个克隆筛选,从装在λ噬菌体载体Charon30中的人基因库中筛选到了一个含人分裂细胞核抗原(PCNA)基因的克隆。经Southern杂交分析插入基因长约14kb,有较长的5'上游区,但3'端缺少一部分。经亚克隆和测序已确定从5'上游1263bp到3'端与λ载体接点共4969bpPCNA基因片段的核苷酸序列。将PCNA基因启动子核苷酸序列与DNA聚合酶α,拓扑异构酶Ⅱα,胸苷酸激酶基因的启动子进行比较有30%以上同源性,具有“看家基因”特征。在转录起始点的5'上游几百bp的范围内都有与CAT,SP1,E2F,NFHB,Oct1和ATF等转录因子的结合位点相似的核苷酸序列。 相似文献
90.
控制大豆白花亲本籽粒脐色的基因有带R与r之分,带R基因的白花产本与紫花亲本杂交,F1代籽料出现蓝脐性状,其基因型为I-R-W1-tt。当控制脐色的基因有两对相差时(R、r;W1、w1)F2代籽粒脐色分离蓝脐与无色脐之比为9∶7。 相似文献