全文获取类型
收费全文 | 4525篇 |
免费 | 463篇 |
国内免费 | 1篇 |
出版年
2023年 | 20篇 |
2022年 | 37篇 |
2021年 | 76篇 |
2020年 | 63篇 |
2019年 | 71篇 |
2018年 | 86篇 |
2017年 | 59篇 |
2016年 | 120篇 |
2015年 | 186篇 |
2014年 | 193篇 |
2013年 | 244篇 |
2012年 | 339篇 |
2011年 | 320篇 |
2010年 | 177篇 |
2009年 | 192篇 |
2008年 | 254篇 |
2007年 | 234篇 |
2006年 | 235篇 |
2005年 | 227篇 |
2004年 | 243篇 |
2003年 | 213篇 |
2002年 | 224篇 |
2001年 | 52篇 |
2000年 | 49篇 |
1999年 | 63篇 |
1998年 | 72篇 |
1997年 | 46篇 |
1996年 | 50篇 |
1995年 | 57篇 |
1994年 | 37篇 |
1993年 | 57篇 |
1992年 | 37篇 |
1991年 | 40篇 |
1990年 | 55篇 |
1989年 | 34篇 |
1988年 | 30篇 |
1987年 | 36篇 |
1986年 | 30篇 |
1985年 | 26篇 |
1984年 | 37篇 |
1983年 | 32篇 |
1982年 | 31篇 |
1981年 | 39篇 |
1980年 | 20篇 |
1979年 | 23篇 |
1978年 | 18篇 |
1977年 | 21篇 |
1976年 | 21篇 |
1974年 | 16篇 |
1973年 | 15篇 |
排序方式: 共有4989条查询结果,搜索用时 15 毫秒
91.
Ellen H. Goldberg Gideon Goldstein Edward A. Boyse Margrit P. Scheid 《Immunogenetics》1981,13(3):201-204
Although young adult C3H/HeJ (OH) females do not reject C3H male skin grafts, OH females older than 1 year commonly do so, as also do many thymectomized, young adult C3H females. Therapy With TP5, a synthetic pentapeptide analogue of thymopoietin which has biological properties of the parent molecule, substantially reduced the capacity of aged OH females and of thymectomized, young OH females to reject OH male skin. 相似文献
92.
Summary In the present study an attempt was made to demonstrate melatonin in the rat pineal gland by means of immunohistochemistry. The anti-body used was raised against 5-methoxy-N-acetyltryptophan which is chemically similar to melatonin. Specific fluorescence was demonstrable only in pineals from rats killed during the night, when melatonin formation is high. It was restricted to parenchymal cells lying in a marginal zone of the organ. These results are discussed in relation to a subdivision of the pineal parenchyma into cortical and medullary areas.Supported by a grant of the Deutsche Forschungsgemeinschaft (VO 135/4) within the Schwerpunktprogramm Neuroendokrinologie 相似文献
93.
Association of long surface appendages with adherence-related functions of the gram-positive species Actinomyces naeslundii 总被引:18,自引:3,他引:15
下载免费PDF全文
![点击此处可从《Journal of bacteriology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Electron microscopy of new isolates of gram-positive Actinomyces naeslundii demonstrated long, fragile appendages. Removal of the appendages impaired attachment to epithelial cells and reaggregation, thus implicating them in attachment-related functions. 相似文献
94.
Ribosomal proteins S3, S4, S7, S20 from Escherichia coli have been studied by small-angle X-ray scattering techniques. The molecular weights found by X-ray scattering agree with other determinations. The large values of the radii of gyration indicate anisometric particles. A more detailed morphological analysis is hindered by low solubility. An interpretation of the experimental results is given in terms of compact objects of simple shape. Yet the possibility is envisaged that these proteins may be less rigid and compact than other proteins. 相似文献
95.
Homogenates from 4-day-old gherkin cotyledons and hypocotyls fractionated by sucrose density gradient centrifugation contain cinnamic acid 4-hydroxylase activity, the activity being highest in the endoplasmic reticulum fractions. These fractions also contain very low concentrations of cytochrome P450. Hydroxylase activity is dependent on NADPH and on molecular oxygen, is optimal at pH 7.5 and is inhibited by carbon monoxide. The enzyme is very sensitive to inhibition by 2-mercaptoethanol, but it is not inhibited by the product, p-coumaric acid. Further, its responses to various potential inhibitors are fairly typical of mixed function oxidases from other sources. 相似文献
96.
97.
The numbers of presumptiveLegionella pneumophila cells in waters and sediments of nine different cooling towers located on the same site in the northeastern United States were determined at approximately monthly intervals for 18 months. All systems received makeup water from the same source and received the same chemical treatments. PresumptiveL. pneumophila were found in both water and sediment samples from all systems on all sampling dates. An important result of this study was the finding that tower sediments represent large reservoirs ofL. pneumophila. The only correlation between levels of presumptiveL. pneumophila and any of the physical, chemical, or operating characteristics evaluated was with winter shutdown and drainage followed by a nonoperational period. These systems showed a definite seasonal response with the highest levels of presumptiveL. pneumophila found in the summer and fall. Systems operated year round showed relatively constant numbers ofL. pneumophila in both water and sediments. 相似文献
98.
Toshiaki Shinohara Michael W. Thomas Ellen G. Gilliam Virginia P. Wray Earl F. Walborg 《Archives of biochemistry and biophysics》1982,219(2):411-421
Novikoff hepatocellular carcinoma cells possess cell-surface glycoproteins that bind the lectin, concanavalin A. A subset of Con A-binding plasma membrane glycoproteins was solubilized by addition of n-butanol to a suspension of Novikoff cells. Glycoproteins solubilized into the n-butanol-saturated aqueous phase of the two-phase mixture were purified by sequential chromatography on DEAE-cellulose and Sepharose-conjugated concanavalin A. Glycoproteins specifically bound to the Sepharose-conjugated Con A exhibited apparent Mr = 72,000 to 125,000. The plasma membrane localization of these components was inferred by their isolation from cells surface labeled with NaIO4/ NaB3H4. A xenoantiserum, raised against glycoproteins specifically bound to Sepharose-conjugated concanavalin A was employed to identify reactive components in nonionic detergent extracts of Novikoff tumor cells or rat hepatocytes surface labeled using lactoperoxidase-catalyzed iodination (125I). Major reactive peptides in extracts of Novikoff cells exhibited apparent Mr = 74,000, 82, 000, 110,000, and 135,000, while those in extracts of hepatocytes possessed apparent Mr = 98,000 and 105,000. The reactivity of the antiserum with extracts of 125I-labeled Novikoff cells was abolished by absorption of the antiserum with hepatocytes, indicating that the qualitative differences observed may result from structural modification of one or more cell-surface glycoproteins, rather than the expression of new or inappropriate glycoproteins. This antiserum will provide a useful probe to investigate alterations in the expression or structure of glycoproteins that occur as a consequence of malignant transformation or adaptation of malignant cells to growth in the ascitic form. 相似文献
99.
Sequence of the clathrin heavy chain from Saccharomyces cerevisiae and requirement of the COOH terminus for clathrin function 总被引:8,自引:0,他引:8
下载免费PDF全文
![点击此处可从《The Journal of cell biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The sequence of the clathrin heavy chain gene, CHC1, from Saccharomyces cerevisiae is reported. The gene encodes a protein of 1,653 amino acids that is 50% identical to the rat clathrin heavy chain (HC) (Kirchhausen, T., S. C. Harrison, E. P. Chow, R. J. Mattaliano, R. L. Ramachandran, J. Smart, and J. Brosius. 1987. Proc. Natl. Acad. Sci. USA. 84:8805-8809). The alignment extends over the complete length of the two proteins, except for a COOH-terminal extension of the rat HC and a few small gaps, primarily in the globular terminal domain. The yeast HC has four prolines in the region of the rat polypeptide that was proposed to form the binding site for clathrin light chains via an alpha-helical coiled-coil interaction. The yeast protein also lacks the COOH-terminal Pro-Gly rich segment present in the last 45 residues of the rat HC, which were proposed to be involved in the noncovalent association of HCs to form trimers at the triskelion vertex. To examine the importance of the COOH terminus of the HC for clathrin function, a HC containing a COOH-terminal deletion of 57 amino acids (HC delta 57) was expressed in clathrin-deficient yeast (chc1-delta). HC delta 57 rescued some of the phenotypes (slow growth at 30 degrees, genetic instability, and defects in mating and sporulation) associated with the chc1-delta mutation to normal or near normal. Also, truncated HCs were assembled into triskelions. However, cells with HC delta 57 were temperature sensitive for growth and still displayed a major defect in processing of the mating pheromone alpha-factor. Fewer coated vesicles could be isolated from cells with HC delta 57 than cells with the wild-type HC. This suggests that the COOH-terminal region is not required for formation of trimers, but it may be important for normal clathrin-coated vesicle structure and function. 相似文献
100.
Evidence that Porphyromonas (Bacteroides) gingivalis fimbriae function in adhesion to Actinomyces viscosus. 总被引:7,自引:0,他引:7
下载免费PDF全文
![点击此处可从《Journal of bacteriology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Porphyromonas (Bacteroides) gingivalis adheres to gram-positive bacteria, such as Actinomyces viscosus, when colonizing the tooth surface. However, little is known of the adhesins responsible for this interaction. A series of experiments were performed to determine whether P. gingivalis fimbriae function in its coadhesion with A. viscosus. Fimbriae typical of P. gingivalis were isolated from strain 2561 (ATCC 33277) by the method of Yoshimura et al. (F. Yoshimura, K. Takahashi, Y. Nodasaka, and T. Suzuki, J. Bacteriol. 160:949-957, 1984) in fractions enriched with a 40-kDa subunit, the fimbrillin monomer, P. gingivalis-A. viscosus coaggregation was inhibited by purified rabbit antifimbrial immunoglobulin G (IgG) at dilutions eightfold higher than those of preimmune IgG, providing indirect evidence implicating P. gingivalis fimbriae in coadhesion. Three types of direct binding assays further supported this observation. (i) Mixtures of isolated P. gingivalis fimbriae and A. viscosus WVU627 cells were incubated for 1 h, washed vigorously with phosphate-buffered saline (pH 7.2), and subjected to electrophoresis. Transblots onto nitrocellulose were probed with antifimbrial antiserum. Fimbrillin labeled positively on these blots. No reaction occurred with the control protein, porcine serum albumin, when blots were exposed to anti-porcine serum albumin, (ii) A. viscosus cells incubated with P. gingivalis fimbriae were agglutinated only after the addition of antifimbrial antibodies. (iii) Binding curves generated from an enzyme immunoassay demonstrated concentration-dependent binding of P. gingivalis fimbriae to A. viscosus cells. From these lines of evidence, P. gingivalis fimbriae appear to be capable of binding to A. viscosus and mediating the coadhesion of these species. 相似文献