全文获取类型
收费全文 | 9916篇 |
免费 | 845篇 |
国内免费 | 10篇 |
专业分类
10771篇 |
出版年
2022年 | 56篇 |
2021年 | 109篇 |
2020年 | 52篇 |
2019年 | 73篇 |
2018年 | 102篇 |
2017年 | 91篇 |
2016年 | 160篇 |
2015年 | 264篇 |
2014年 | 341篇 |
2013年 | 466篇 |
2012年 | 554篇 |
2011年 | 565篇 |
2010年 | 388篇 |
2009年 | 362篇 |
2008年 | 563篇 |
2007年 | 553篇 |
2006年 | 536篇 |
2005年 | 555篇 |
2004年 | 515篇 |
2003年 | 540篇 |
2002年 | 485篇 |
2001年 | 128篇 |
2000年 | 135篇 |
1999年 | 187篇 |
1998年 | 169篇 |
1997年 | 138篇 |
1996年 | 123篇 |
1995年 | 108篇 |
1994年 | 108篇 |
1993年 | 98篇 |
1992年 | 115篇 |
1991年 | 112篇 |
1990年 | 112篇 |
1989年 | 105篇 |
1988年 | 108篇 |
1987年 | 64篇 |
1986年 | 73篇 |
1985年 | 86篇 |
1984年 | 109篇 |
1983年 | 87篇 |
1982年 | 108篇 |
1981年 | 95篇 |
1980年 | 84篇 |
1979年 | 62篇 |
1978年 | 73篇 |
1977年 | 76篇 |
1976年 | 59篇 |
1975年 | 64篇 |
1974年 | 59篇 |
1973年 | 67篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
B A Bernard J M Bernardon C Delescluse B Martin M C Lenoir J Maignan B Charpentier W R Pilgrim U Reichert B Shroot 《Biochemical and biophysical research communications》1992,186(2):977-983
The action of retinoids on gene regulation is mediated by three distinct nuclear retinoic acid receptor (RAR) subtypes called RAR alpha, beta and gamma. Since RAR gamma is predominantly expressed in adult skin, specific ligands for this subtype could (i) represent valuable tools to evaluate the biological role of RAR gamma in skin and (ii) provide therapeutic entities with a higher therapeutic index at lower teratogenic risk. Using in vitro binding studies and a functional transactivation assay, we have identified three compounds with high RAR gamma selectivity. 相似文献
52.
53.
Petrus Jakobus van Zyl Bernard Alexander Prior 《Applied microbiology and biotechnology》1990,33(1):12-17
Summary Glycerol and arabitol were the main polyols accumulated by Zygosaccharomyces rouxii in continuous culture but the intracellular and extracellular concentrations of the polyols varied with the dilution rate and osmoticum used to adjust the water activity (aw) to 0.960. When the aw was adjusted with NaCl, glycerol was the main polyol accumulated intracellularly whereas glycerol and arabitol were accumulated when polyethylene glycol (PEG) 400 was used. The extracellular glycerol and arabitol concentrations at 0.960 aw (NaCl or PEG 400) were similar or decreased relative to cultures at 0.998 aw. Compared to steady-state cultivation at 0.998 aw, the yeast retained at 0.960 aw (NaCl or PEG 400) a greater proportion of the total glycerol intracellularly against an increased concentration ratio without significantly greater production of glycerol. Arabitol was only significant in osmoregulation when cultivated at 0.960 aw (PEG 400). The intracellular glycerol concentration was insufficient to balance the aw across the membrane, but an equilibrium could be achieved under certain conditions if arabitol was also osmotically active.
Offprint requests to: P. J. van Zyl 相似文献
54.
Preparation and characterization of human interleukin-5 expressed in recombinant Escherichia coli. 总被引:2,自引:0,他引:2 下载免费PDF全文
A E Proudfoot D Fattah E H Kawashima A Bernard P T Wingfield 《The Biochemical journal》1990,270(2):357-361
The gene coding for human interleukin-5 was synthesized and expressed in Escherichia coli under control of a heat-inducible promoter. High-level expression, 10-15% of total cellular protein, was achieved in E. coli. The protein was produced in an insoluble state. A simple extraction, renaturation and purification scheme is described. The recombinant protein was found to be a homodimer, similar to the natural murine-derived protein. Despite the lack of glycosylation, high specific activities were obtained in three 'in vitro' biological assays. Physical characterization of the protein showed it to be mostly alpha-helical, supporting the hypothesis that a conformational similarity exists among certain cytokines. 相似文献
55.
Bernard L. Strehler 《Photosynthesis research》1996,48(1-2):11-18
The circumstances that led to the discovery that plants luminesce after they are illuminated are described, as are other discoveries that would not have been possible were it not for the fortuitous association I had with my dear and most admirable friend, W.A. Arnold, to whom this special issue is dedicated. 相似文献
56.
Hanne Gahéry-Ségard Evelyne Jouvin-Marche Adrien Six Carine Gris-Liebe Marie Malissen Bernard Malissen Pierre-André Cazenave Patrice N. Marche 《Immunogenetics》1996,44(4):298-305
The number of mouse Tcra-V gene segments varies from one individual to another and is estimated to be about 100. Southern blot analysis revealed that
most of the Tcra-V are organized in clusters composed of copies of Tcra-V belonging to different subfamilies. We analyzed in detail a Tcra-V subfamily and looked for new Tcra-V in order to improve the knowledge of the mouse Tcra locus organization. A series of genomic clones derived from the B10.A mouse strain enclosing these clusters was used to determined
the structure of all the Tcra-V2. We were able to identify ten Tcra-V2. This study showed that the Tcra-V2 can be organized into three structural subgroups. The distribution of the genes along the Tcra locus, plus their structural organization, indicates that successive duplications occurred during the processes of expansion
and contraction of the Tcra-V gene subfamilies. Several Tcra-V2 are also identical, indicating recent duplications. The most divergent Tcra-V2 differ by 7.4% nucleotides, leading to 5.2% differences in amino acid contents.
Received: 8 August 1995 / Revised: 24 April 1996 相似文献
57.
Spermiogenesis in M. herpestisbegins with the formation of a differentiation zone which contains two centrioles associated with an electron–dense, finely granular material. This granular material very quickly becomes striated, a median cytoplasmic extension forms, one of the centrioles becomes laterally oriented in a cytoplasmic bud and the other gives rise to a flagellum. After the migration of the nucleus, a helicoidal crested–like body forms, then the old spermatid separates from the residual cytoplasm. The mature M. herpestisspermatozoon exhibits an apical cone of electron–dense material, a crested–like body and cortical microtubules which are electron–dense centred and spiralized except at their posterior extremity where they are parallel to the spermatozoon axis. The axoneme is of the 9 + ‘1’ pattern. It reaches the posterior extremity of the gamete where the cytoplasm is very electron–dense. The presence of centrioles flanked by ‘striated roots’ has never, to our knowledge, been reported in a platyhelminth. Likewise, a nucleus with an annular cross–section and unevenly distributed electron–dense peri–axonemal material has never been described in a cestod. 相似文献
58.
Michael Dean J. Claiborne Stephens Cheryl Winkler Deborah A. Lomb Mark Ramsburg Raleigh Boaze Claudia Stewart Lauren Charbonneau David Goldman Bernard J. Albaugh James J. Goedert R. Palmer Beasley Lu-Yu Hwang Susan Buchbinder Michael Weedon Patricia A. Johnson Mary Eichelberger Stephen J. O'Brien 《American journal of human genetics》1994,55(4):788-808
A panel of 257 RFLP loci was selected on the basis of high heterozygosity in Caucasian DNA surveys and equivalent spacing throughout the human genome. Probes from each locus were used in a Southern blot survey of allele frequency distribution for four human ethnic groups: Caucasian, African American, Asian (Chinese), and American Indian (Cheyenne). Nearly all RFLP loci were polymorphic in each group, albeit with a broad range of differing allele frequencies (δ). The distribution of frequency differences (δ values) was used for three purposes: (1) to provide estimates for genetic distance (differentiation) among these ethnic groups, (2) to revisit with a large data set the proportion of human genetic variation attributable to differentiation within ethnic groups, and (3) to identify loci with high δ values between recently admixed populations of use in mapping by admixture linkage disequilibrium (MALD). Although most markers display significant allele frequency differences between ethnic groups, the overall genetic distances between ethnic groups were small (.066–.098), and <10% of the measured overall molecular genetic diversity in these human samples can be attributed to “racial” differentiation. The median δ values for pairwise comparisons between groups fell between .15 and .20, permitting identification of highly informative RFLP loci for MALD disease association studies. 相似文献
59.
Indigenous Arbuscular Mycorrhizal Fungi Associated with Acacia albida Del. in Different Areas of Senegal 下载免费PDF全文
Tahir A. Diop Mamadou Gueye Bernard L. Dreyfus Christian Plenchette Desire G. Strullu 《Applied microbiology》1994,60(9):3433-3436
The influences of seasons, plant age, and physicochemical properties of the soil on surface and deep biological arbuscular mycorrhizal fungus parameters associated with Acacia albida were assessed in different areas of Senegal. More indigenous arbuscular mycorrhizal propagules were found in the localities of the Sudano-Guinean zone (Djinaki and Kabrousse) than in those of the Sahelian zone (Louga and Diokoul), and species belonging to the genera Glomus, Gigaspora, Acaulospora, and Sclerocystis prevailed. The numbers of total and viable spores increased more during the rainy season than during the dry season (about 108% more total spores and 262% more viable spores). Similarly, both total and viable spores were more prevalent around young Acacia trees than old trees. However, the intensities of root colonization did not differ in each ecoclimatic zone. 相似文献
60.
Catherine L. Craig Gary D. Bernard Jonathan A. Coddington 《Evolution; international journal of organic evolution》1994,48(2):287-296
We measured the reflectance properties of unpigmented silks spun by a systematic array of primitive (Deinopoidea) and derived (Araneoidea) aerial, web-spinning spiders, as well as silks spun by Araneomorphae and Mygalomorphae spiders that do not spin aerial webs. Our data show that all of the primitive aerial web spinners produce catching silks with a spectral peak in the ultraviolet (UV), and cladistic analysis suggests that high UV reflection is the primitive character state for silk spectral properties. In contrast, all of the derived aerial web spinners produce silks that are spectrally flat or characterized by reduced reflectance in the UV. Correlated with the evolution of these catching silks is a 37-fold increase in species number and apparent habitat expansion. This suggests that the unique silk proteins spun by the araneoids have been important to their ecological and evolutionary diversity. 相似文献