首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   7992篇
  免费   486篇
  国内免费   1篇
  8479篇
  2022年   47篇
  2021年   75篇
  2020年   28篇
  2019年   61篇
  2018年   85篇
  2017年   76篇
  2016年   137篇
  2015年   219篇
  2014年   237篇
  2013年   504篇
  2012年   405篇
  2011年   416篇
  2010年   247篇
  2009年   286篇
  2008年   415篇
  2007年   382篇
  2006年   443篇
  2005年   407篇
  2004年   456篇
  2003年   382篇
  2002年   401篇
  2001年   214篇
  2000年   199篇
  1999年   201篇
  1998年   111篇
  1997年   114篇
  1996年   84篇
  1995年   75篇
  1994年   96篇
  1993年   80篇
  1992年   117篇
  1991年   120篇
  1990年   116篇
  1989年   97篇
  1988年   94篇
  1987年   83篇
  1986年   113篇
  1985年   93篇
  1984年   95篇
  1983年   75篇
  1982年   64篇
  1981年   61篇
  1980年   50篇
  1979年   59篇
  1978年   51篇
  1977年   41篇
  1976年   38篇
  1975年   22篇
  1974年   33篇
  1973年   28篇
排序方式: 共有8479条查询结果,搜索用时 9 毫秒
61.
Yeast strains were isolated from dried sweet potatoes (hoshi-imo), a traditional preserved food in Japan. Dough fermentation ability, freeze tolerance, and growth rates in molasses, which are important characteristics of commercial baker's yeast, were compared between these yeast strains and a commercial yeast derivative that had typical characteristics of commercial strains. Classification tests including pulse-field gel electrophoresis and fermentation/assimilation ability of sugars showed that almost the stains isolated belonged to Saccharomyces cerevisiae. One strain, ONY1, accumulated intracellular trehalose at a higher level than commercial strain T128. Correlated with intracellular trehalose contents, the fermentation ability of high-sugar dough containing ONY1 was higher. ONY1 also showed higher freeze tolerance in both low-sugar and high-sugar doughs. The growth rate of ONY1 was significantly higher under batch and fed-batch cultivation conditions using either molasses or synthetic medium than that of strain T128. These results suggest that ONY1 has potential commercial use as baker's yeast for frozen dough and high-sugar dough.  相似文献   
62.
Using structure-based drug design, we identified and optimized a novel series of pyrimidodiazepinone PLK1 inhibitors resulting in the selection of the development candidate TAK-960. TAK-960 is currently undergoing Phase I evaluation in adult patients with advanced solid malignancies.  相似文献   
63.
Bornavirus, a non-segmented, negative-strand RNA viruses, is currently classified into several genetically distinct genotypes, such as Borna disease virus (BDV) and avian bornaviruses (ABVs). Recent studies revealed that bornavirus genotypes show unique sequence variability in the putative 5′ untranslated region (5′ UTR) of X/P mRNA, a bicistronic mRNA for the X protein and phosphoprotein (P). In this study, to understand the evolutionary relationship among the bornavirus genotypes, we investigated the functional interaction between the X and P proteins of four bornavirus genotypes, BDV, ABV genotype 4 and 5 and reptile bornavirus (RBV), the putative 5′ UTRs of which exhibit variation in the length. Immunofluorescence and immunoprecipitation analyses using mammalian and avian cell lines revealed that the X proteins of bornaviruses conserve the ability to facilitate the export of P from the nucleus to the cytoplasm via interaction with P. Furthermore, we showed that inter-genotypic interactions may occur between X and P among the genotypes, except for X of RBV. In addition, a BDV minireplicon assay demonstrated that the X and P proteins of ABVs, but not RBV, can affect the polymerase activity of BDV. This study demonstrates that bornaviruses may have conserved the fundamental function of a regulatory protein during their evolution, whereas RBV has evolved distinctly from the other bornavirus genotypes.  相似文献   
64.
This study was undertaken to investigate whether the concentration of carbonic anhydorase isoenzyme I (CA-I) in canine feces and urine is useful as a temporary marker of occult blood. Concentrations of CA-I were measured by enzyme-linked immunosorbent assay (ELISA). Fecal CA-I concentrations in 113 healthy beagle dogs (50 male and 63 female) of various ages ranged from 4.3 to 16.7 ng/g feces (mean; 7.0 +/- 2.9 ng/g feces). One milliliter of blood from 3 healthy beagle dogs was found to contain 1,047, 1,062 and 1,150 microg CA-I. The fecal CA-I concentrations of dogs receiving intragastric infusions of autologous blood (10 ml) were very low. However, the fecal CA-I concentrations of dogs receiving infusion of autologous blood (5 ml) into the ascending colon were very high. Detection of fecal CA-I would be useful for identifying dogs with hemorrhaging of the large intestine. Of 55 urinary samples collected from healthy beagle dogs by catheter, chemical tests for occult blood were negative in 44, but CA-I concentrations ranged from 1.8 to 12.6 ng/ml (mean; 6.9 +/- 5.4 ng/ml) by ELISA. The CA-I concentrations of the other 11 samples, which tested positive for occult blood on chemical testing, ranged from 41.2 to 525.0 ng/ml by ELISA. Although CA-I is not a specific marker of erythrocytes, CA-I may be used to detect occult blood in canine feces and urine until a specific immunological test kit using antibody for Hb is developed.  相似文献   
65.
Carbachol (CCh), a muscarinic-cholinergic agonist, increased both cytosolic free calcium concentration ([Ca2+]i) and amylase release in rat parotid acinar cells or acini in a dose-dependent manner. Treatment of acinar cells with the intracellular Ca2+ antagonist, 8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate (TMB-8), or the intracellular Ca2+ chelator, 1,2-bis(O-aminophenoxy)ethane-N,N,N'N'-tetraacetic acid (BAPTA), strongly attenuated the increases in [Ca2+]i evoked by CCh, but amylase release from acini was not significantly suppressed by the treatment with TMB-8 or BAPTA. Low concentrations (0.02-0.5 microM) of ionomycin, a Ca2+ ionophore, caused increases in [Ca2+]i comparable to those induced by CCh, but the same concentrations had only a little effect on amylase release. The protein kinase C activator, 12-O-tetradecanoylphorbol-13-acetate (TPA), stimulated amylase release in quantities similar to those induced by CCh, although TPA alone did not cause any change in [Ca2+]i. Combined addition of TPA and ionomycin potentiated only modestly amylase release stimulated by TPA alone. Staurosporine, a protein kinase C-inhibitor, similarly inhibited both the CCh- and TPA-induced amylase release. These results suggest that an increase in [Ca2+]i elicited by CCh does not play an essential role for inducing amylase release in rat parotid acini. Amylase release by muscarinic stimulation may be mediated mainly by activation of protein kinase C.  相似文献   
66.
We identified human decapping enzyme 2 (hDCP2) as a binding protein with Ro52, being colocalized in processing bodies (p-bodies). We also showed that the N-terminus and C-terminus of Ro52 bound to hDCP2. Moreover, Ro52 enhanced decapping activity of hDCP2 in a dose-dependent manner. Our data support the novel notion of the association between Ro52 with hDCP2 protein in cytoplasmic p-bodies, playing a role in mRNA metabolism in response to cellular stimulation.  相似文献   
67.
Symplastic intercellular transport in plants is achieved by plasmodesmata (PD). These cytoplasmic channels are well known to interconnect plant cells to facilitate intercellular movement of water, nutrients, and signaling molecules including hormones. However, it is not known whether Al may affect this cell-to-cell transport process, which is a critical feature for roots as organs of nutrient/water uptake. We have microinjected the dye lucifer yellow carbohydrazide into peripheral root cells of an Al-sensitive wheat (Triticum aestivum cv Scout 66) either before or after Al treatment and followed the cell-to-cell dye-coupling through PD. Here we show that the Al-induced root growth inhibition is closely associated with the Al-induced blockage of cell-to-cell dye coupling. Immunofluorescence combined with immuno-electron microscopic techniques using monoclonal antibodies against 1-->3-beta-D-glucan (callose) revealed circumstantial evidence that Al-induced callose deposition at PD may responsible for this blockage of symplastic transport. Use of 2-deoxy-D-glucose, a callose synthesis inhibitor, allowed us to demonstrate that a reduction in callose particles correlated well with the improved dye-coupling and reduced root growth inhibition. While assessing the tissue specificity of this Al effect, comparable responses were obtained from the dye-coupling pattern in tobacco (Nicotiana tabacum) mesophyll cells. Analyses of the Al-induced expression of PD-associated proteins, such as calreticulin and unconventional myosin VIII, showed enhanced fluorescence and co-localizations with callose deposits. These results suggest that Al-signal mediated localized alterations to calcium homeostasis may drive callose formation and PD closure. Our data demonstrate that extracellular Al-induced callose deposition at PD could effectively block symplastic transport and communication in higher plants.  相似文献   
68.
To elucidate the exact role of the PGD(2) system in sleep-wake regulation in vivo, the sleep behavior of knockout mice, generated in the author's and other laboratories, was examined for lipocalin-type PGD synthase (L-PGDS), PGD receptor, adenosine A(2A) receptor, and histamine H(1) receptor; transgenic mice overexpressing the human L-PGDS gene, generated in the author's laboratory, were also examined. The circadian profiles of sleep patterns of wild-type and the genetically manipulated mice were essentially identical, indicating the possibility that the deficiency of one system may be effectively compensated by some other systems during development. Available evidence indicated that the PGD(2) system is involved in the homeostatic regulation of non-rapid eye movement sleep and that the arousal effect of orexin A is mediated by the histamine H(1) receptor system.  相似文献   
69.
70.
A highly sensitive quantitative PCR detection method has been developed and applied to the distribution analysis of human intestinal bifidobacteria by combining real-time PCR with Bifidobacterium genus- and species-specific primers. Real-time PCR detection of serially diluted DNA extracted from cultured bifidobacteria was linear for cell counts ranging from 10(6) to 10 cells per PCR assay. It was also found that the method was applicable to the detection of Bifidobacterium in feces when it was present at concentrations of >10(6) cells per g of feces. Concerning the distribution of Bifidobacterium species in intestinal flora, the Bifidobacterium adolescentis group, the Bifidobacterium catenulatum group, and Bifidobacterium longum were found to be the three predominant species by examination of DNA extracted from the feces of 46 healthy adults. We also examined changes in the population and composition of Bifidobacterium species in human intestinal flora of six healthy adults over an 8-month period. The results showed that the composition of bifidobacterial flora was basically stable throughout the test period.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号