全文获取类型
收费全文 | 4754篇 |
免费 | 284篇 |
国内免费 | 3篇 |
出版年
2023年 | 14篇 |
2022年 | 17篇 |
2021年 | 51篇 |
2020年 | 28篇 |
2019年 | 37篇 |
2018年 | 56篇 |
2017年 | 56篇 |
2016年 | 104篇 |
2015年 | 147篇 |
2014年 | 163篇 |
2013年 | 294篇 |
2012年 | 275篇 |
2011年 | 259篇 |
2010年 | 190篇 |
2009年 | 169篇 |
2008年 | 285篇 |
2007年 | 290篇 |
2006年 | 255篇 |
2005年 | 269篇 |
2004年 | 239篇 |
2003年 | 223篇 |
2002年 | 213篇 |
2001年 | 125篇 |
2000年 | 120篇 |
1999年 | 85篇 |
1998年 | 57篇 |
1997年 | 44篇 |
1996年 | 46篇 |
1995年 | 50篇 |
1994年 | 23篇 |
1993年 | 22篇 |
1992年 | 63篇 |
1991年 | 64篇 |
1990年 | 52篇 |
1989年 | 86篇 |
1988年 | 64篇 |
1987年 | 47篇 |
1986年 | 45篇 |
1985年 | 66篇 |
1984年 | 32篇 |
1983年 | 37篇 |
1982年 | 38篇 |
1981年 | 15篇 |
1980年 | 23篇 |
1979年 | 23篇 |
1978年 | 19篇 |
1977年 | 21篇 |
1975年 | 17篇 |
1974年 | 15篇 |
1973年 | 19篇 |
排序方式: 共有5041条查询结果,搜索用时 31 毫秒
81.
K Tamura M Kobayashi Y Ishii T Tamura K Hashimoto S Nakamura M Niwa J Zapf 《The Journal of biological chemistry》1989,264(10):5616-5621
Rat insulin-like growth factor-I (IGF-I), a serum polypeptide with growth promoting activity, was isolated from rat serum by a combination of acid/ethanol extraction, affinity chromatography, and a series of reversed phase high performance liquid chromatography, cation exchange, and reversed phase. All peptide fragments produced by chymotrypsin digestion of reduced and carboxymethylated rat IGF-I were amino acid sequenced and compared with the sequence of human IGF-I. Three out of 70 of the rat amino acid residues differed from those of human IGF-I as follows: Asp20----Pro, Ser35----Ile and Ala67----Thr. Purified rat IGF-I cross-reacted with polyclonal anti-human IGF-I antibody 75% as compared to human IGF-I, but it cross-reacted only 3% with monoclonal anti-human IGF-I antibody. Thus, it is possible to monitor the metabolic fate of human IGF-I, when injected into rats, without interference by endogenous rat IGF-I. Rat IGF-I showed 65% activity in the radioreceptor, 28.6% activity in the lipogenesis and 22.5% activity in the free fatty acid release inhibition assays as compared to human IGF-I on a protein quantity basis. 相似文献
82.
Experimental Angiostrongylus costaricensis infection was carried out in inbred strains of mice (C57BL/6 BALB/c, DBA/2 and C3H/He). All strains became infected with this parasite. Marked differences in mortality and in worm burden were found among inbred strains of mice tested. A significant reduction was shown in worm length from mice compared to that from cotton rats. 相似文献
83.
Two dynorphin-degrading cysteine proteases, I and II, were extracted with Triton X-100 from neuroblastoma cell membrane, isolated from accompanying dynorphin-degrading trypsin-like enzyme by affinity chromatography on columns of soybean trypsin inhibitor-immobilized Sepharose and p-mercuribenzoate-Sepharose, and separated by ion-exchange chromatography on diethylaminoethyl (DEAE)-cellulose and TSK gel DEAE-5PW columns. Cysteine protease II was purified further by hydroxyapatite chromatography and gel filtration. The molecular weights of cysteine proteases I and II were estimated to be 100,000 and 70,000, respectively, by gel filtration. Both of the enzymes, were inhibited by p-chloromercuribenzoate, N-ethylmaleimide, and high-molecular-weight kininogen, but not or only slightly inhibited by diisopropylphosphorofluoridate, antipain, leupeptin, E-64, calpain inhibitor, and phosphoramidon. Cysteine protease I cleaved dynorphin(1-17) at the Arg6-Arg7 bond with the optimum pH of 8.0, whereas II cleaved dynorphin(1-17) at the Lys11-Leu12 bond and the Leu12-Lys13 bond with the optimum pH values of 8.0 and 6.0, respectively. These bonds corresponded to those that had been proposed as the initial sites of degradation by neuroblastoma cell membrane. Cysteine protease I was further found to show strict specificity toward the Arg-Arg doublet, when susceptibilities of various peptides containing paired basic residues were examined as substrates for the enzyme. 相似文献
84.
M Kuboki H Ishii S Horie M Kazama 《Biochemical and biophysical research communications》1992,185(3):1122-1127
Thrombin stimulation of platelets resulted in changes in the subcellular localization of calpain I, with a concomitant alteration of its molecular weight as measured by immunoblotting. Calpain I in resting platelets was distributed as procalpain I, an 80 kDa form which does not exhibit the enzyme activity, and 83% of the total antigen was localized in the cytosol fraction. When platelets were stimulated with thrombin, the total content of calpain I antigen was not significantly changed as compared with that of the resting platelets, though a decrease in the cytosolic distribution of 80 kDa form (from 83% to 47% of the total antigen) was observed with concomitant appearance of the active 76 kDa and intermediate 78 kDa forms of calpain I and increase in the 80 kDa form in the granule and membrane fractions. These results indicated that calpain I was translocated from the cytosol to both the plasma and granule membranes as procalpain I and then activated on the membranes during platelet stimulation with thrombin. 相似文献
85.
Structures and properties of seven isoforms of the NMDA receptor generated by alternative splicing. 总被引:19,自引:0,他引:19
H Sugihara K Moriyoshi T Ishii M Masu S Nakanishi 《Biochemical and biophysical research communications》1992,185(3):826-832
We here report the existence of 6 additional isoforms of the NMDA receptor generated via alternative splicing by molecular analysis of cDNA clones isolated from a rat forebrain cDNA library. These isoforms possess the structures with an insertion at the extracellular amino-terminal region or deletions at two different extracellular carboxyl-terminal regions, or those formed by combinations of the above insertion and deletions. One of the deletions results in the generation of a new carboxyl-terminal sequence. All these isoforms possess the ability to induce electrophysiological responses to NMDA and respond to various antagonists selective to the NMDA receptor in the Xenopus oocyte expression system. In addition, a truncated form of the NMDA receptor also exists that contains only the extreme amino-terminal sequence of this protein molecule. These data indicate that the NMDA receptor consists of heterogeneous molecules that differ in the extracellular sequence of the amino- and carboxyl-terminal regions. 相似文献
86.
Yuichi Mazaki Makoto Mochii Ryuji Kodama Goro Eguchi 《Development, growth & differentiation》1996,38(4):429-437
When retinal pigmented epithelial cells (PEC) of chick embryos are cultured under appropriate conditions, the phenotype changes to that of lens cells through a process known as transdifferentiation. The first half of the process, characterized by dedifferentiation of PEC, is accompanied by a marked decrease in adhesiveness of PEC to collagen type I- or type IV-coated dishes. To understand the underlying mechanisms of this change, we analyzed the expression of integrins, which are major receptors for extracellular matrix components. Northern blot analysis with cDNA probes for chicken α3, α6, α8, αv, β1 and β5 integrin mRNA showed that the genes for all these integrins are transcribed at similar levels in PEC and dedifferentiated PEC (dePEC). Further analysis of β1 integrin, which is a major component of integrin heterodimers, showed that although the protein amount of β1 integrin was not changed, its localization at focal contacts seen in PEC was lost in dePEC. When anti-β1 integrin antibody was added to the PEC culture medium, a decrease of cell-substrate adhesiveness occurred, followed by a gradual change in both morphology and gene expression patterns to ones similar to those of dePEC. These findings suggest that an appropriate distribution of β1 integrin plays an essential role in maintaining the differentiated state of PEC through cell-substrate adhesion. 相似文献
87.
Shinji Yamasaki Zaw Lin Hiromasa Shirai Akito Terai Yuichi Oku Hideaki Ito Mari Ohmura Tadahiro Karasawa Teizo Tsukamoto Hisao Kurazono Yoshifumi Takeda 《Microbiology and immunology》1996,40(5):345-352
To identify the type of Verotoxins (VT) produced by Verocytotoxin-producing Escherichia coli (VTEC), a sensitive bead-enzyme-linked immunosorbent assay and polymerase chain reaction with common and specific primers to various VTs (VT1, VT2, VT2vha, VT2vhb, and VT2vp1) were developed. Together with colony hybridization tests with oligo- and polynucleotide probes, these methods were applied to VTEC isolates to type the VT produced. The toxin types of 26 of 37 strains were identified, but the reaction profiles in assays of the remaining 11 strains suggested the existence of new VT2 variants. The application of these identification procedures may be useful as a tool for clinical and epidemiological studies of VTEC infection. 相似文献
88.
Yuichi Murayama Ryozaburo Mukai Tetsutaro Sata Satoko Matsunaga Atsuo Noguchi Yasuhiro Yoshikawa 《Microbiology and immunology》1996,40(6):467-471
In contrast to the case of peripheral T cells, the surface expression of CD20 antigen and the expression of CD20 mRNA in monkey lymph node (LN) T cells underwent a noticeable increase when they were cultured with mitogen and interleukin-2 (IL-2). To confirm in vivo regulation of CD20 expression during the activation of LN T cells, we examined LNs derived from monkeys experimentally inoculated with simian immunodeficiency virus (SIV). Significant expression of CD20 antigen was detected in the T cells of the LNs at the stage of lymphadenopathy. These findings suggest that lymphocyte activation in the LNs induced expression of the CD20 molecule in some T cells. 相似文献
89.
Takeuchi Yuichi; Murakami Mina; Nakajima Nobuyoshi; Kondo Noriaki; Nikaido Osamu 《Plant & cell physiology》1996,37(2):181-187
Photoinduced lesions in DNA, namely, cyclobutane pyrimidinedimers (CPDs) and pyrimidine-(6-4)-pyrimidone photoproducts[(6-4)photoproducts], in cucumber cotyledons that had been irradiatedwith naturally occurring levels of UV-B (290320 nm) werequantitated by enzyme-linked immunosorbent assays with monoclonalantibodies specific to each type of photolesion. Induction ofthese photolesions was dependent on temperature and their extentwas reduced by simultaneous irradiation with white light. Thedark repair of both types of photolesion was undetectable. Light-dependentremoval of (6-4)photoproducts was very slow, with 50% removalin 4 h. By contrast, 50% of initial CPDs were removed within15 min. Both photorepair processes were dependent on the intensityof white light and were sensitive to temperature. These resultsindicate that high photolyase activity is present in cucumbercotyledons and that repair activities in cucumber cotyledonsare different from those reported in Arabidopsis, in which (6-4)photoproductsare photorepaired more rapidly than CPDs. (Received October 13, 1995; Accepted December 28, 1995) 相似文献
90.
Carrot (Daucus carota L.) embryogenic callus (EC) loses its embryogenic competence and becomes nonembryogenic callus (NC) during long-term culture. With the loss of embryogenic competence, the cell clusters become smaller and the extent of intercellular attachments is reduced. Pectic fractions prepared from EC and NC were separated into two subfractions by gel filtration. A difference in sugar composition between EC and NC was found only in the high-molecular-mass (ca. 1300 kDa) subfraction, and the ratio of the amount of arabinose to that of galactose (Ara/Gal) was strongly and positively correlated with the size of cell clusters in several different cultures. From the results of sugar-composition and methylation analyses, and the results of treatment with exo-arabinanase, models of the neutral sugar chains of pectins from EC and NC are proposed. Both neutral sugar chains are composed of three regions. The basal region is composed of linearly linked arabinan 5-Araf> moieties in both types of callus. The middle galactan region is composed of 6-linked galactose, some of which branches at the 3 and 4 positions, and this region is larger and more frequently branched in NC than in EC. Finally, the terminal arabinan region is composed of 5-linked arabinose, branched at the 3 position, and the size of the terminal arabinan is larger in EC than in NC. The significance of the neutral sugar chains of pectins in the interaction of cell wall components and intercellular attachment is discussed.Abbreviations Ara/Gal
ratio (w/w) of the amount of arabinose to that of galactose
- EC
embryogenic callus
- NC
non-embryogenic callus
- T-Araf
terminal arabinose
The authors are grateful to Dr. Naoto Shibuya of the National Institute of Agrobiological Resources for his gift of exo-arabinanase. 相似文献