全文获取类型
收费全文 | 22127篇 |
免费 | 1752篇 |
国内免费 | 7篇 |
出版年
2023年 | 197篇 |
2022年 | 217篇 |
2021年 | 500篇 |
2020年 | 412篇 |
2019年 | 394篇 |
2018年 | 732篇 |
2017年 | 644篇 |
2016年 | 775篇 |
2015年 | 867篇 |
2014年 | 937篇 |
2013年 | 1301篇 |
2012年 | 1833篇 |
2011年 | 1860篇 |
2010年 | 973篇 |
2009年 | 788篇 |
2008年 | 1439篇 |
2007年 | 1473篇 |
2006年 | 1399篇 |
2005年 | 1156篇 |
2004年 | 1136篇 |
2003年 | 1052篇 |
2002年 | 897篇 |
2001年 | 301篇 |
2000年 | 370篇 |
1999年 | 256篇 |
1998年 | 147篇 |
1997年 | 121篇 |
1996年 | 117篇 |
1995年 | 106篇 |
1994年 | 103篇 |
1993年 | 88篇 |
1992年 | 129篇 |
1991年 | 99篇 |
1990年 | 75篇 |
1989年 | 89篇 |
1988年 | 61篇 |
1987年 | 62篇 |
1986年 | 41篇 |
1985年 | 51篇 |
1984年 | 83篇 |
1983年 | 53篇 |
1982年 | 65篇 |
1981年 | 55篇 |
1980年 | 57篇 |
1979年 | 39篇 |
1978年 | 46篇 |
1977年 | 38篇 |
1976年 | 38篇 |
1975年 | 40篇 |
1974年 | 36篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
Recent studies demonstrated that deglycosylation step is a prerequisite for endoplasmic reticulum (ER)-associated degradation of misfolded glycoproteins. Here, we report the advantages of using benzyl mannose during pulse-chase experiments to study the subcellular location of the deglycosylation step in Chinese hamster ovary (CHO) cell lines. Benzyl mannose inhibited both the ER-to-cytosol transport of oligomannosides and the trimming of cytosolic-labeled oligomannosides by the cytosolic mannosidase in vivo. We pointed out the occurrence of two subcellular sites of deglycosylation. The first one is located in the ER lumen, and led to the formation of Man8GlcNAc2 (isomer B) in wild-type CHO cell line and Man4GlcNAc2 in Man-P-Dol-deficient cell line. The second one was revealed in CHO mutant cell lines for which a high rate of glycoprotein degradation was required. It occurred in the cytosol and led to the liberation of oligosaccharides species with one GlcNAc residue and with a pattern similar to the one bound onto glycoproteins. The cytosolic deglycosylation site was not specific for CHO mutant cell lines, since we demonstrated the occurrence of cytosolic pathway when the formation of truncated glycans was induced in wild-type cells. 相似文献
972.
973.
Age estimation of unknown skeletal remains is very important in forensic medicine. Morphologic methods are fast and easy to use for purpose of age determination. The sternal ends of the ribs are a reliable method of age estimation from late adolescence to old age. Iscan et al developed a phase analysis method for the right 4th rib that was sex and race specific. The purpose of this study is to determine the accuracy of the standards of age estimation from the right 4th and other rib using the phase analysis for the Turkish population. The sample consisted of right and left 3rd, 4th and 5th ribs from 34 Turkish women and 76 men. There were statistically significant variations found on the right 5th, left 3rd, 4th, and 5th ribs according to these standards in men for phases 5, 6, and 7. For women, all the right and left ribs included in this study were in concordance with right 4th rib standards in all phases. 相似文献
974.
This study targets development of an effective training scheme model that can be implemented at elementary school level with focus on recovery and recycling of wasted papers in Turkey. For this purpose, three schools were chosen from a district within Istanbul. They were separated from one another as full intervention (FI), semi-intervention (SI) and control (C) schools. Different levels of educational activities carried out in the schools, mostly in the FI school, were directed toward being informative as regards recycling and the development of a positive attitude. Afterwards, in order to evaluate the effects of the training, paper wastes were collected in recycle bins placed at appropriate points in schools and weighed on a weekly basis. Quite a significant result was found (p = 0.0001), when the difference was calculated through the Kruskal Wallis Variance Analysis method, regarding the weekly average amount of paper in each of the three schools against per person. Furthermore, when the results were evaluated and compared as to the ones before the 2.5 months summer vacation and the ones after it, the seven measurements taken before (p = 0.001) and the eight taken afterwards (p = 0.0001), were found to have valid differences, once again, as against schools. The results show that the approach we provided to education is an effective method not only for the collection of paper wastes but also for applications in various areas of health education. 相似文献
975.
Olivares EL Ribeiro VP Werneck de Castro JP Ribeiro KC Mattos EC Goldenberg RC Mill JG Dohmann HF dos Santos RR de Carvalho AC Masuda MO 《American journal of physiology. Heart and circulatory physiology》2004,287(2):H464-H470
Postinfarct congestive heart failure is one of the leading causes of morbidity and mortality in developed and developing countries. The main purpose of this study was to investigate whether transplantation of bone marrow stromal cells (BMSC) directly into the myocardium could improve the performance of healed infarcted rat hearts. Cell culture medium with or without BMSC was injected into borders of cardiac scar tissue 4 wk after experimental infarction. Cardiac performance was evaluated 2 wk after cellular (n = 10) or medium (n = 10) injection by electro- and echocardiography. Histological study was performed 3 wk after treatment. Electrocardiography of BMSC-treated infarcted rats showed electrical and mechanical parameters more similar to those in control than in medium-treated animals: a normal frontal QRS axis in 6 of 10 BMSC-treated and all control rats and a rightward deviation of the QRS axis in all 10 medium-treated animals. BMSC treatment, assessed by echocardiography, improved fractional shortening (39.00 +/- 4.03%) compared with medium-treated hearts (18.20 +/- 0.74%) and prevented additional changes in cardiac geometry. Immunofluorescence microscopy revealed colocalization of 4',6-diamidino-2-phenylindole-labeled nuclei of transplanted cells with cytoskeletal markers for cardiomyocytes and smooth muscle cells, indicating regeneration of damaged myocardium and angiogenesis. These data provide strong evidence that BMSC implantation can improve cardiac performance in healed infarctions and open new promising therapeutic opportunities for patients with postinfarction heart failure. 相似文献
976.
Deinococcus radiodurans possesses an exceptional capacity to withstand the lethal and mutagenic effects of most form of DNA damage and has received considerable interest for use in both fundamental and applied research. Here we describe vectors that allow regulated expression of Deinococcal genes for functional analysis. The vectors contain the IPTG-regulated Spac system (Pspac promoter and lacI repressor gene), originally designed for Bacillus subtilis, that we have adapted to be functional in D. radiodurans. We show that the Spac system can control the expression of a lacZ reporter gene over two orders of magnitude depending on the inducer concentration and the copy number of the lacI regulatory gene. Furthermore, we demonstrate that the Spac system can be used to regulate the synthesis of a critical repair protein, such as RecA, resulting in a conditional mitomycin-resistant cell phenotype. We have also developed tools for the construction of conditional mutants where the expression of the target gene is regulated by an inducible promoter. The utility of these conditional gene inactivation systems is exemplified by the conditional lethal phenotype of a mutant expressing gyrA from the Pspac promoter. 相似文献
977.
Early weaning is a technique used to increase swine health status, and may cause consequences in reproductive performance of sows. An experiment was performed to evaluate these effects in a herd of sows, with weaning at 9 or 10 days post-farrowing, located in west of Minas Gerais, Brazil. Large-White sows (n=102), with three or four previous parturitions were randomly allocated to three treatment groups: T1: artificial insemination (AI) at first post-weaning estrus of the sows; T2: AI at second post-weaning estrus, T3: AI at first estrus, after an administration of a daily individual dose of 20 mg of altrenogest from 5 to 8 days post-weaning. The duration of the first post-weaning estrus did not differ among treatment groups; however, the second estrus of the T2 group was of shorter duration relative to the other treatment groups (P< or =0.035). Ovulation occurred earlier at the second estrus of the T2 group, compared with the T1 and T3 groups (P< or =0.027), being similar to that at the first estrus of T2 group (P=0.177). The relationship of the timing between ovulation and estrus was similar among treatment groups (P> or =0.221). There was no difference in farrowing rate among treatment groups (P> or =0.313). The T2 group produced a mean of 2.5 more piglets per litter (P=0.002). In conclusion, the use of altrenogest did not increase the reproductive performance of early-weaned sows. 相似文献
978.
Lima M Almeida J Teixeira MA Santos AH Queirós ML Fonseca S Moura J Gonçalves M Orfão A Pinto Ribeiro AC 《Journal of biological regulators and homeostatic agents》2004,18(3-4):331-334
Several phenotypic changes have been shown to occur after NK-cell stimulation, involving molecules that have been proved to regulate NK-cell migration into tissues and NK-cell activation and proliferation as well as target cell recognition and killing. Here, we review the reactive phenotypes observed in vivo after acute and chronic NK-cell activation. 相似文献
979.
980.
Vincentz M Cara FA Okura VK da Silva FR Pedrosa GL Hemerly AS Capella AN Marins M Ferreira PC França SC Grivet L Vettore AL Kemper EL Burnquist WL Targon ML Siqueira WJ Kuramae EE Marino CL Camargo LE Carrer H Coutinho LL Furlan LR Lemos MV Nunes LR Gomes SL Santelli RV Goldman MH Bacci M Giglioti EA Thiemann OH Silva FH Van Sluys MA Nobrega FG Arruda P Menck CF 《Plant physiology》2004,134(3):951-959