全文获取类型
收费全文 | 40778篇 |
免费 | 4402篇 |
国内免费 | 12篇 |
专业分类
45192篇 |
出版年
2022年 | 308篇 |
2021年 | 541篇 |
2020年 | 353篇 |
2019年 | 430篇 |
2018年 | 558篇 |
2017年 | 529篇 |
2016年 | 918篇 |
2015年 | 1650篇 |
2014年 | 1602篇 |
2013年 | 2112篇 |
2012年 | 2405篇 |
2011年 | 2125篇 |
2010年 | 1468篇 |
2009年 | 1337篇 |
2008年 | 1861篇 |
2007年 | 1816篇 |
2006年 | 1626篇 |
2005年 | 1592篇 |
2004年 | 1491篇 |
2003年 | 1289篇 |
2002年 | 1284篇 |
2001年 | 1227篇 |
2000年 | 1230篇 |
1999年 | 1110篇 |
1998年 | 608篇 |
1997年 | 564篇 |
1996年 | 558篇 |
1995年 | 536篇 |
1994年 | 489篇 |
1993年 | 512篇 |
1992年 | 1003篇 |
1991年 | 749篇 |
1990年 | 770篇 |
1989年 | 751篇 |
1988年 | 652篇 |
1987年 | 596篇 |
1986年 | 609篇 |
1985年 | 707篇 |
1984年 | 530篇 |
1983年 | 412篇 |
1982年 | 340篇 |
1981年 | 312篇 |
1980年 | 253篇 |
1979年 | 378篇 |
1978年 | 343篇 |
1977年 | 241篇 |
1976年 | 225篇 |
1975年 | 196篇 |
1974年 | 289篇 |
1973年 | 250篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
201.
202.
203.
Peter Kaastrup René J. M. Stet Albert J. Tigchelaar Egbert Egberts Willem B. van Muiswinkel 《Immunogenetics》1989,30(4):284-290
In this study, experiments are described that were designed to investigate whether fish have an immune regulatory systems
similar to the major histocompatibility complex (MHC) in higher vertebrate species. From combinations of gynogenetic carp
showing either slow of fast rejection of skin transplants, the latter were chosen for alloantiserum production by hyperimmunization
with peripheral blood leucocytes. The resulting alloantisera were analyzed for hemagglutinating reactivity with gynogenetic
siblings and proved to be operationally monoscpecific in absorption experiments. The serologically determined carp erythrocyte
specificites were shown to correspond to two codominantly expressed allelic products of a single locus and were designated
K1 and K2, respectively. Flow cytometer analysis revealed that the same products are also present on leucocytes from peripheral
blood, thymus, spleen, and pronephros.K1-andK2-homozygous second-generation gynogenetic siblings were used to study the histocompatibiligy nature of the K locus products.
Skin transplants between K-allogeneic gynogenetic siblings were rejected significantly faster than within K-syngeneic combinations.
Taken together, these data suggest that theK locus incorporates MHC class I-like characteristics. 相似文献
204.
The antigens belonging to the HLA-A10 group, HLA-A25, -A26, -Aw34, and -Aw66, have been characterized serologically during the International Histocompatibility Workshops. However, it remains difficult to discriminate between the HLA-A26 antigen on the one hand and the HLA-Aw34 and -Aw66 antigens on the other on the basis of serology. In this paper, we compare the serologically defined antigens with the data obtained by one-dimensional isoelectric focusing. The results indicate that the serologically well-defined HLA-A25 antigen cannot be discriminated from the HLA-A26 antigen by one-dimensional isoelectric focusing. In contrast, this technique can indeed be used to discriminate between HLA-A26, -Aw34 and -Aw66 antigens. In addition, the biochemical analysis suggests further heterogeneity of the HLA-Aw34 antigen. This antigen can be subdivided into three variants. 相似文献
205.
Transient expression of the proto-oncogene int-1 during differentiation of P19 embryonal carcinoma cells. 总被引:6,自引:2,他引:4 下载免费PDF全文
In mouse embryos, the int-1 proto-oncogene is transiently expressed in areas of the developing neural system. Retinoic acid-treated P19 embryonal carcinoma cells have often been used as an in vitro model for the molecular basis of neural development. We shown here that int-1 is transiently expressed in differentiated P19 cells. The time course and retinoic acid dose dependence of int-1 expression suggest that the gene is specifically expressed during early neural differentiation. P19 cells may be a useful model to assist in the study, at the cellular level, of the role of int-1 in neural development. 相似文献
206.
Accumulation of viruslike particles in a yeast mutant lacking a mitochondrial pore protein. 总被引:9,自引:4,他引:5 下载免费PDF全文
M Dihanich E van Tuinen J D Lambris B Marshallsay 《Molecular and cellular biology》1989,9(3):1100-1108
The lack of mitochondrial porin is not lethal in Saccharomyces cerevisiae, but it impairs some respiratory functions and, therefore, growth on nonfermentable carbon sources such as glycerol. However, after a lag phase porinless mutant cells adapt to growth on glycerol, accumulating large amounts of an 86-kilodalton (kDa) protein (M. Dihanich, K. Suda, and G. Schatz, EMBO J. 6:723-728, 1987) and of a 5-kilobase RNA. Immunogold labeling localized the 86 kDa-protein exclusively to the cytosol fraction, although most of it cosedimented with the microsome fraction in earlier cell fractionations. This discrepancy was resolved when the 86-kDa protein was identified as the major coat protein in viruslike particles (VLPs) which is encoded by a double-stranded RNA (L-A RNA). Elimination of VLPs in the original porinless strain by introduction of the mak10 or the mak3 mutation increased the respiratory defect and prolonged its lag phase on nonfermentable carbon sources. The fact that the simultaneous loss of VLPs and respiratory functions are the introduction of mak10 or mak3 occurred even in some porin-containing wild-type strains suggests that there is a link between VLP and mitochondrial functions. 相似文献
207.
The Editors of Letters in Applied Microbiology will, at their discretion, publish invited and submitted 'Opinions' on subjects in the general area of Applied Microbiology. They will not be subjected to the normal refereeing procedures and reprints will not be provided. The 'Opinions' will not necessarily represent the views of the Society for Applied Bacteriology or of the Editors. The Editors may invite or readers may submit 'Responses' to published 'Opinions' , provided that they are not merely polemics, and these will also be published at the discretion of the Editors. 'Responses' will be treated precisely like 'Opinions'. They should clearly indicate, in their first sentence, the 'Opinion' to which they are a response. 相似文献
208.
We have identified the domain of the human c-myc protein (c-Myc) produced in Escherichia coli that is responsible for the ability of the protein to bind sequence-nonspecific DNA. Using analysis of binding of DNA by proteins transferred to nitrocellulose, DNA-cellulose chromatography, and a nitrocellulose filter binding assay, we examined the binding properties of c-Myc peptides generated by cyanogen bromide cleavage, of mutant c-Myc, and of proteins that fuse portions of c-Myc to staphylococcal protein A. The results of these analyses indicated that c-Myc amino acids 265 to 318 were responsible for DNA binding and that other regions of the protein (including a highly conserved basic region and a region containing the leucine zipper motif) were not required. Some mutant c-Mycs that did not bind DNA maintained rat embryo cell-cotransforming activity, which indicated that the c-Myc property of in vitro DNA binding was not essential for this activity. These mutants, however, were unable to transform established rat fibroblasts (Rat-1a cells) that were susceptible to transformation by wild-type c-Myc, although this lack of activity may not have been due to their inability to bind DNA. 相似文献
209.
Aida van Gelderen de Komaid 《Mycopathologia》1989,105(2):111-116
A previous analysis of the physiological properties of Nocardia brasiliensis strains isolated from soil of Tucumán proves that non-pathogenic strains have a different behaviour pattern from the pathogenic strains.In the present paper, 16 Nocardia brasiliensis strains isolated from human mycetomas were studied in the same way. The object is to determine if any of the Nocardia brasiliensis present in soil can produce human mycetomas.The macro and micromorphological, biochemical (17 tests), physiological (4 tests) and pathological characteristics were determined for each of the strains. Experimental pathogenicity was determined using albino Swiss mice by inoculation into the footpads.The strains of Nocardia brasiliensis that cause human mycetomas have the same physiological pattern and experimental pathogenicity as the virulent strains present in soil. 相似文献
210.
C. M. B. Duwel F. C. Visser M. J. van Eenige J. P. Roos 《Molecular and cellular biochemistry》1989,88(1-2):191-194
Summary Under normal and ischemic conditions backdiffusion of radiolabeled non-esterified fatty acids (NEFA) has been demonstrated. In the fasted normal canine heart the extraction fraction (EF) during interventions with glucose or lactate loading, vasodilation, and metabolic level augmentation was determined, and compared with the control EF. Backdiffusion alterations were deduced from the EF changes. After iv injection of 17-iodo-131 heptadecanoic acid (IHDA), 11 blood samples were drawn from aorta and coronary sinus in a time period of 60 minutes. In the control and vasodilation group the EF slowly decreased from 40 to 10%. In contrast, the EF in the noradrenaline group was constant. During glucose and lactate infusion the EF became negative within 10 min and remained negative. These results suggest that during physiological circumstances backdiffusion is determined by the metabolic level of the heart and its substrate availability. 相似文献