全文获取类型
收费全文 | 19141篇 |
免费 | 1413篇 |
国内免费 | 1515篇 |
专业分类
22069篇 |
出版年
2024年 | 48篇 |
2023年 | 330篇 |
2022年 | 658篇 |
2021年 | 1088篇 |
2020年 | 670篇 |
2019年 | 905篇 |
2018年 | 802篇 |
2017年 | 560篇 |
2016年 | 877篇 |
2015年 | 1153篇 |
2014年 | 1457篇 |
2013年 | 1519篇 |
2012年 | 1808篇 |
2011年 | 1565篇 |
2010年 | 989篇 |
2009年 | 847篇 |
2008年 | 942篇 |
2007年 | 809篇 |
2006年 | 658篇 |
2005年 | 578篇 |
2004年 | 484篇 |
2003年 | 436篇 |
2002年 | 387篇 |
2001年 | 285篇 |
2000年 | 290篇 |
1999年 | 303篇 |
1998年 | 195篇 |
1997年 | 199篇 |
1996年 | 188篇 |
1995年 | 151篇 |
1994年 | 136篇 |
1993年 | 96篇 |
1992年 | 140篇 |
1991年 | 114篇 |
1990年 | 100篇 |
1989年 | 77篇 |
1988年 | 52篇 |
1987年 | 31篇 |
1986年 | 28篇 |
1985年 | 41篇 |
1984年 | 18篇 |
1983年 | 23篇 |
1982年 | 12篇 |
1981年 | 7篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1965年 | 1篇 |
1963年 | 1篇 |
1962年 | 1篇 |
1950年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Two bacterial symbionts of entomopathogenic nematodes, one of which originated from Texas, U.S.A., and the other from Newfoundland, Canada, were characterized phenotypically. These strains belonged to the genus Xenorhabdus. The Newfoundland (NF) strain was shown to be X. bovienii but the Texas (TX) strain was not identified at the species level. Four additional cultures of Xenorhabdus were included in the study. These were a strain of X. bovienii (Ume?), which was from a nematode of European origin, and strains of X. nematophilus, X. beddingii, and X. poinarii. The tests used in this study indicated identical properties for the NF (North American) and Ume? (European) strains of X. bovienii. These could be differentiated from the other strains studied by their failure to grow at 34 degrees C and resistance to low concentrations of a mixture of amoxilline and clavulanic acid. The Xenorhabdus TX strain could be differentiated from the other strains studied by its failure to grow at 10 degrees C. Of the tests done, approximately 30 were useful in distinguishing between the strains and species studied. 相似文献
72.
To identify salt stress-responsive genes, we constructed a cDNA library with the salttolerant rice cultivar, Lansheng. About 15000 plasmids were extracted and dotted on filters with Biomeck 2000 HDRT system or by hand. Thirty genes were identified to display altered expression levels responding to 150 mmol/L NaCl. Among them eighteen genes were up-regulated and the remainders downregulated. Twenty-seven genes have their homologous genes in GenBank Databases. The expression of twelve genes was studied by Northern analysis. Based on the functions, these genes can be classified into five categories, including photosynthesis-related gene, transportrelated gene, metabolismrelated gene, stress-or resistancerelated gene and the others with various functions. The results showed that salt stress influenced many aspects of rice growth. Some of these genes may play important roles in plant salt tolerance. 相似文献
73.
为评估定量荧光PCR(QF-PCR)方法在男性不育遗传学诊断中的应用价值,文章对78例非梗阻性男性不育患者,采用精液常规检测精子情况,并检测患者性激素水平;采用QF-PCR方法对患者性染色体多态性STR位点及特异性位点进行检测;采用常规染色体G显带方法进行核型分析;PCR检测AZF微缺失。结果显示78例非梗阻性男性不育患者中发现无精子症患者18例,少精子症患者20例,总检出率为48.72%。采用QF-PCR方法检出3例47,XXY患者,2例46,XX(SRY+)性反转患者,1例AZFc区微缺失患者,与细胞培养染色体分析和AZF微缺失PCR检测结果相符。与传统方法相比,QF-PCR技术能更迅速、直接、可靠地检测到男性不育患者的染色体异常区域,及早发现染色体细微结构异常,有助于染色体异常造成的男性不育症的鉴别诊断。 相似文献
74.
自行制备一种新型生物素-亲和素偶联探针分子并用于反相蛋白芯片的检测。首先, 将生物素-羊抗鼠IgG与亲和素按照不同比例混合后与鼠IgG蛋白芯片反应, 观察荧光信号的放大情况; 然后以鼠IgG-羊抗鼠IgG体系为研究模式, 对反相蛋白芯片的制备条件进行了考察和优化, 包括荧光分子的非特异性吸附、点样缓冲液的选择以及蛋白的活性等。最后, 采用此偶联探针对反相蛋白芯片进行了检测。结果表明, BSA缓冲液制备的反相蛋白芯片可以防止非特异性吸附, 并有利于保持固定蛋白活性和提高检测限; 另外, 与传统的与生物素-亲和素检测技术相比, 采用生物素-亲和素偶联探针对反相芯片的检测限可以提高4倍左右。表明亲和素-生物素偶联探针成本低、易于合成、并可以与其它的信号放大技术联用进一步提高检测的灵敏度, 有望用于蛋白质芯片的检测。 相似文献
75.
Novel chiral ionic liquids stationary phases for the enantiomer separation of chiral acid by high‐performance liquid chromatography 下载免费PDF全文
Novel chiral ionic liquid stationary phases based on chiral imidazolium were prepared. The ionic liquid chiral selector was synthesized by ring opening of cyclohexene oxide with imidazole or 5,6‐dimethylbenzimidazole, and then chemically modified by different substitute groups. Chiral stationary phases were prepared by bonding to the surface of silica sphere through thioene “click” reaction. Their enantioselective separations of chiral acids were evaluated by high‐performance liquid chromatography. The retention of acid sample was related to the counterion concentration and showed a typical ion exchange process. The chiral separation abilities of chiral stationary phases were greatly influenced by the substituent group on the chiral selector as well as the mobile phase, which indicated that, besides ion exchange, other interactions such as steric hindrance, π‐π interaction, and hydrogen bonding are important for the enantioselectivity. In this report, the influence of bulk solvent components, the effects of varying concentration, and the type of the counterion as well as the proportion of acid and basic additives were investigated in detail. 相似文献
76.
Xiong XH Han S Wang JH Jiang ZH Chen W Jia N Wei HL Cheng H Yang YX Zhu B You S He JY Hou W Chen MX Yu CJ Jiao YH Zhang WC 《Journal of bacteriology》2011,193(1):315-316
Ketogulonicigenium vulgare is characterized by the efficient production of 2KGA from L-sorbose. Ketogulonicigenium vulgare Y25 is known as a 2-keto-L-gulonic acid-producing strain in the vitamin C industry. Here we report the finished, annotated genome sequence of Ketogulonicigenium vulgare Y25. 相似文献
77.
78.
Comparison of mucosal adhesion and species identification of bifidobacteria isolated from healthy and allergic infants 总被引:14,自引:0,他引:14
He F Ouwehand AC Isolauri E Hashimoto H Benno Y Salminen S 《FEMS immunology and medical microbiology》2001,30(1):43-47
Fifty bifidobacteria strains were isolated from fecal samples of allergic and age matched healthy infants. Allergic infants were found to have an adult type Bifidobacterium flora with high levels of Bifidobacterium adolescentis. Healthy infants had a typical infant Bifidobacterium flora with high levels of Bifidobacterium bifidum. These isolates were tested for their adhesive properties to human intestinal mucus. The adhesion of the fecal bifidobacteria from healthy infants was significantly higher (P<0.0001) than for allergic infants. This suggests a correlation between allergic disease and the composition of the intestinal bifidobacteria flora which has reduced adhesive abilities to the intestinal mucus. Therefore, dietary supplementation of bifidobacteria typical for healthy infants, may be beneficial in the treatment of allergic disorders. 相似文献
79.
80.
Mouse thymic stromal cell line 4 (MTSC4) is one of the stromal cell lines established in our laboratory. While losing the characteristics of epithelial cells, they express some surface markers shared with thymic dendritic cells (TDCs). To further study the biological functions of these cells, we compared the capability of MTSC4 with TDCs in the induction of thymocyte apoptosis, using thymic reaggregation culture system. Apoptosis of thymocytes induced by MTSC4 and TDCs was measured by Annexin V and PI staining and analyzed by flow cytometry. We found that MTSC4 selectively augmented the apoptosis of CD4^ 8^ (DP) thymocytes. This effect was Fas/FasL independent and could not be blocked by antibodies to MHC class I and class II molecules. In addition, MTSC4 enhanced the apoptosis of DP thymocytes from different strains of mice, which implies that MTSC4-induced thymocyte apoptosis is not mediated by the TCR recognition of self peptide/MHC molecules. In contrast to MTSC4, thymocyte apoptosis induced by TDCs was MHC-restricted. Thus, MHC-independent fashion of stromal-DP thymocyte interaction may be one of the ways to induce thymocyte apoptosis in thymus. Our study has also shown that the interaction of MTSC4 stromal cells and thymocytes is required for the induction of thymocyte apoptosis. 相似文献