全文获取类型
收费全文 | 2363篇 |
免费 | 176篇 |
国内免费 | 3篇 |
出版年
2022年 | 19篇 |
2021年 | 26篇 |
2020年 | 13篇 |
2019年 | 23篇 |
2018年 | 27篇 |
2017年 | 25篇 |
2016年 | 42篇 |
2015年 | 77篇 |
2014年 | 81篇 |
2013年 | 233篇 |
2012年 | 146篇 |
2011年 | 126篇 |
2010年 | 93篇 |
2009年 | 59篇 |
2008年 | 136篇 |
2007年 | 130篇 |
2006年 | 104篇 |
2005年 | 117篇 |
2004年 | 115篇 |
2003年 | 106篇 |
2002年 | 97篇 |
2001年 | 54篇 |
2000年 | 61篇 |
1999年 | 56篇 |
1998年 | 19篇 |
1997年 | 24篇 |
1996年 | 8篇 |
1995年 | 17篇 |
1994年 | 17篇 |
1993年 | 20篇 |
1992年 | 34篇 |
1991年 | 42篇 |
1990年 | 44篇 |
1989年 | 32篇 |
1988年 | 31篇 |
1987年 | 27篇 |
1986年 | 16篇 |
1985年 | 19篇 |
1984年 | 25篇 |
1983年 | 15篇 |
1982年 | 18篇 |
1981年 | 22篇 |
1980年 | 12篇 |
1979年 | 29篇 |
1978年 | 16篇 |
1977年 | 9篇 |
1976年 | 9篇 |
1975年 | 8篇 |
1974年 | 15篇 |
1973年 | 10篇 |
排序方式: 共有2542条查询结果,搜索用时 15 毫秒
41.
Corrigendum
Upstream regulatory sequences from two -conglycinin genes 相似文献42.
The food habits of the Iriomote catFelis iriomotensis were studied by analyzing 177 feces collected monthly from 1987 to 1988. A total of 26 food items were identified. The frequency
of lizards and frogs in the feces was higher than those of mammals and birds. The food habits changed greatly seasonally.Eumeces skinks were fed on most frequently, and found in the feces with a similar high frequency occurrence in March–April and July–September,
while their proportion to the total number of food items was larger in March–April than in July–September. The cats fed on
larg-sized skinks, adultEumeces kishinouyei, more in March–April than in other seasons. The number of skinks sighted in the course of a road census was greater from
March to August, and large-sized skinks were sighted more in March–April than in July–August. The cats fed selectively on
large-sized skinks in every season. Therefore, changes in the food habits depended on the food availability. Characteristics
of food habits in the Iriomote cat are discussed in comparison with the food habits of other felids in temperate and tropical
regions. 相似文献
43.
Histological studies on male sterility of hybrids between laboratory and wild mouse strains 总被引:1,自引:0,他引:1
Atsushi Yoshiki Kazuo Moriwaki Teruyo Sakakura Moriaki Kusakabe 《Development, growth & differentiation》1993,35(3):271-281
In this study the cellular mechanisms of male sterility in F1 hybrids (BNF1) between BALB/c and wild-derived M.MUS-NJL (NJL) was investigated. Cell proliferation and differentiation in the sterile testis were examined by bromodeoxyuridine-labeling and use of germ cell stage-specific antibodies. In BNF1 testes, spermatogonia actively proliferated with a seminiferous epithelial cycle, and were retained in the basal layer of the tubules. However, preleptotene, leptotene and zygotene spermatocytes moved to the adluminal region. Immunohistological data with germ cell stage-specific antibodies indicated the presence of few, if any, pachytene spermatocytes in BNF1 testes. Thus, spermatogenesis seemed to be blocked at the zygotene stage. For examination of germ cell-Sertoli cell interactions, testes of aggregation chimeras between BNF1 and C3H/HeN were analyzed immunohistologically with C3H-specific antibody. Results showed that spermatogenesis of C3H-germ cells was normal, even when these cells in contact with BNF1-Sertoli cells. Differentiation of BNF1-germ cells progressed from zygotene to pachytene stage spermatocytes when these cells were surrounded by C3H-Sertoli cells, but never proceeded beyond the pachytene stage. These observations suggest that at least two different cellular factors may be involved in spermatogenesis, one acting in the germ cells and the other mediated by Sertoli cells. Furthermore, mating experiments revealed that the degree of spermatogenesis varied in different F1 hybrids, and that the major sterility factor was closely linked to the T -locus on chromosome 17. 相似文献
44.
A model for feature linking via collective oscillations in the primary visual cortex 总被引:2,自引:0,他引:2
Tsuyoshi Chawanya Toshio Aoyagi Ikuko Nishikawa Koji Okuda Yoshiki Kuramoto 《Biological cybernetics》1993,68(6):483-490
A neural network model for explaining experimentally observed neuronal responses in cat primary visual cortex is proposed. In our model, the basic functional unit is an orientation column which is represented by a large homogeneous population of neurons modeled as integrate-and-fire type excitable elements. The orientation column exhibits spontaneous collective oscillations in activity in response to suitable visual stimuli. Such oscillations are caused by mutual synchronization among the neurons within the column. Numerical simulation for various stimulus patterns shows that as a result of activity correlations between different columns, the amplitude and the phase of the oscillation in each column depend strongly on the global feature of the stimulus pattern. These results satisfactorily account for experimental observations. 相似文献
45.
Toshiyuki Takahashi Hiroshi Ishikura Kazuhiro Iwai Chisa Takahashi Hiroyuki Kato Tatsuzo Tanabe Takashi Yoshiki 《Cancer immunology, immunotherapy : CII》1993,36(2):76-82
The permanent pancreas carcinoma cell line, PCI-24, was developed in order to analyse cytokine regulation on pancreas carcinoma and lymphokine-activated killer (LAK) cell interaction. PCI cells expressed ICAM-1 and HLA-ABC, but not HLA-DR antigens. PCI cells showed augmented ICAM-1 and HLA-ABC expression when incubated with interferon (IFN) and tumour necrosis factor . A similar but weak augmentary effect on the HLA-ABC and ICAM-1 surface expression was seen with interleukin-1 treatment. Natural attachment of LAK to PCI cells was augmented by recombinant IFN in close association with ICAM-1 up-regulation on PCI cells. In addition, natural attachment was significantly inhibited by anti-LFA-1 and anti-ICAM-1 antibody treatments. Cytotoxicity of the LAK cells against PCI cells was also significantly inhibited with the same treatment. Thus, the attachment of LAK cells to PCI cells through LFA-1/ICAM-1 molecules appeared to be essential for the cytotoxicity for PCI cells. Pretreatment of PCI cells, but not of LAK cells, with IFN or other cytokines resulted in a decrease of susceptibility for LAK cell cytotoxicity. The decreased susceptibility inversely correlated with HLA-ABC expression on the PCI cells. The collective evidence indicates that, although LAK cell attachment to pancreas carcinoma cells through the LFA-1/ICAM-1 molecule is augmented by IFN, IFN treatment of pancreas carcinoma cells reduces LAK cell cytotoxicity possibly through an increase in HLA-ABC or a regulation of molecules closely associated to HLA-ABC expression. 相似文献
46.
47.
Masahiro Sakaguchi Sakae Inouye Yuichi Takahashi Susumu Kutagiri Hiroshi Yasueda 《Aerobiologia》1995,11(4):265-268
We examined the kinetics of airborne levels of mite allergen particles in a house by combined use of an indoor Burkard air
sampler and immunoblotting. Airborne mite allergens collected on the Burkard sampling tape were transferred onto a nitrocellulose
membrane, reacted with mouse monoclonal anti-mite allergen (Der pI) antibody, then treated with alkaline phosphatase conjugated anti-mouse IgG. Finally, the blotted allergen on the membrane
was reacted with BCIP/NBT phosphatase, and purple spots visible by the naked eye were produced. The shape of the spots was
observed under a microscope, and the spot area was measured by an image processor. This technique might be useful for analyzing
the behavior of airborne allergen particles in indoor environments. 相似文献
48.
Novel DNA binding proteins highly specific to UV-damaged DNA sequences from embryos of Drosophila melanogaster. 总被引:1,自引:0,他引:1
下载免费PDF全文
![点击此处可从《Nucleic acids research》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Three new proteins which selectively bind to UV-damaged DNA were identified and purified to near homogeneity from UV-irradiated Drosophila melanogaster embryos through several column chromatographies. These proteins, tentatively designated as D-DDB P1, P2 and P3, can be identified as different complex bands in a gel shift assay by using UV-irradiated TC-31 probe DNA. Analysis of the purified D-DDB P1 fraction by native or SDS-polyacrylamide gel electrophoresis and FPLC-Superose 6 gel filtration demonstrated that it is a monomer protein which is a 30 kDa polypeptide. The D-DDB P2 protein is a monopolypeptide with a molecular mass of 14 kDa. Both D-DDB P1 and P2 highly prefer binding to UV-irradiated DNA, and have almost no affinity for non-irradiated DNA. Gel shift assays with either UV-irradiated DNA probes demonstrated that D-DDB P1 may show a preference for binding to (6-4) photoproducts, while D-DDB P2 may prefer binding to pyrimidine dimers. Both these proteins require magnesium ions for binding. D-DDB P1 is an ATP-preferent protein. These findings are discussed in relation to two recently described [Todo and Ryo (1991) Mutat. Res., 273, 85-93; Todo et al. (1993) Nature, 361, 371-374] DNA-binding factors from Drosophila cell extracts. A possible role for these DNA-binding proteins in lesion recognition and DNA-binding proteins in lesion recognition and DNA repair of UV-induced photo-products is discussed. 相似文献
49.
50.
Two forms of -glucosidase (EC 3.2.1.20), designated as I and II, have been isolated from sugarbeet (Beta vulgaris L.) seeds by a procedure including fractionation with ammonium sulfate and ethanol, carboxymethyl-cellulose column chromatography, and preparative disc gel electrophoresis. The two enzymes were homogeneous by polyacrylamide disc gel electrophoresis. Their molecular weights were 98,000 (I) and 60,000 (II). -Glucosidase I readily hydrolyzed maltose, isomaltose, kojibiose, maltotriose, panose, amylose, soluble starch, amylopectin and glycogen. -Glucosidase II also hydrolyzed maltose, kojibiose and maltotriose but hydrolyzed the other substrates only very weakly or not at all. -Glucosidase I hydrolyzed soluble starch at a faster rate than maltose. It produced isomaltose and panose as the main -glucosyltransfer products from maltose, whereas maltotriose was the main product of -glucosidase II. -Glucosidase I hydrolyzed amylose liberating -glucose. The neutral-sugar content was calculated to be 2.7% for -glucosidase I and 8.8% for -glucosidase II. The main neutral sugar was mannose in -glucosidase I, and glucose in -glucosidase II. 相似文献