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   10320篇
  免费   866篇
  国内免费   2篇
  2022年   43篇
  2021年   93篇
  2020年   55篇
  2019年   73篇
  2018年   114篇
  2017年   106篇
  2016年   152篇
  2015年   233篇
  2014年   284篇
  2013年   611篇
  2012年   472篇
  2011年   491篇
  2010年   298篇
  2009年   271篇
  2008年   480篇
  2007年   505篇
  2006年   466篇
  2005年   505篇
  2004年   488篇
  2003年   456篇
  2002年   460篇
  2001年   338篇
  2000年   377篇
  1999年   350篇
  1998年   135篇
  1997年   105篇
  1996年   123篇
  1995年   108篇
  1994年   109篇
  1993年   124篇
  1992年   288篇
  1991年   191篇
  1990年   209篇
  1989年   207篇
  1988年   317篇
  1987年   191篇
  1986年   155篇
  1985年   142篇
  1984年   114篇
  1983年   93篇
  1982年   78篇
  1981年   67篇
  1979年   80篇
  1978年   65篇
  1977年   46篇
  1976年   51篇
  1975年   49篇
  1974年   63篇
  1973年   43篇
  1972年   53篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
171.
Amino acid sequences of fibrinopeptides A and B from the macaque, Macaca fuscata (Japanese monkey) and the guenon, Erythrocebus patas (patas monkey) were established. Fibrinopeptides A of the monkeys had a sequence identical with those of baboons: Ala-Asp-Thr-Gly-Glu-Gly-Asp-Phe-Leu-Ala-Glu-Gly-Gly-Gly-Val-Arg. Fibrinopeptides B were 9-residue, "short," peptides with the sequences Asn-Glu-Glu-Ser-Leu-Phe-Ser-Gly-Arg for M. fuscata and Asn-Glu-Glu-Val-Leu-Phe-Gly-Gly-Arg for E. patas. The sequence of the B peptide of M. fuscata differed from that of a close-related species, M. mulatta (rhesus monkey), at a single site, Leu (M.f.)----Pro (M.m.). A single replacement between the B peptides of E. patas and Cercocebus aethiops (green monkey), Val (E.p.)----Gly (C.a.), was detected. A phylogenic relationship of macaques, guenons, and baboons, named Cercopithecinae (Old World monkey), was deduced from the sequence data. A selective rather than random amino acid replacement was observed in the B peptides of these Old World monkeys, suggesting a restricted mutation of their fibrinopeptides during primate evolution.  相似文献   
172.
The giant extracellular hemoglobin from the polychaete Tylorrhynchus heterochaetus consists of two types of subunits: a "monomeric" chain (chain I) and a disulfide-bonded trimer of chains IIA, IIB, and IIC. The complete amino acid sequence of chain IIB was determined. This chain has 148 amino acid residues and a molecular weight of 17,236 including a heme group. Of the residues in chain IIB, 74 (50%) and 34 (30%) were found to be identical with those in the corresponding positions in Tylorrhynchus chains IIC and I, respectively (Suzuki, T., Furukohri, T., and Gotoh, T. (1985) J. Biol. Chem. 260, 3145-3154). Marked differences were found between the chains of Tylorrhynchus and Lumbricus in the COOH-terminal regions. Significant differences were predicted between the monomeric chain I and the "trimeric" chains (IIB and IIC) in the hydropathy profiles and alpha-helical contents.  相似文献   
173.
A major glycosphingolipid in rat bone marrow cells was purified, and its structure was studied. The glycolipid was found to exhibit blood group B activity by the hemagglutination inhibition test. The structure was determined to be (formula; see text) by studies of nuclear magnetic resonance, sequential hydrolysis by exoglycosidases, linkage analysis of methylated sugars by gas chromatography-mass spectrometry, and immunological tests. The blood group B active glycolipid was detected not only in the bone marrow cells but also in spleen, thymus, and rat ascites hepatoma AH 7974F cells. Besides the glycolipid, gangliotriaosylceramide, gangliotetraosylceramide, and fucogangliotetraosylceramide were commonly detected in these cells. The similarity between the glycolipid species on the cell surfaces of the immunocytes and the tumor cells is discussed with the respect to an escape mechanism of the tumor cells from the immunosurveillance system.  相似文献   
174.
The phosphorylation of phosphoinositides in the acetylcholine receptor (AChR)-rich membranes from the electroplax of the electric fish Narke japonica has been examined. When the AChR-rich membranes were incubated with [gamma-32P]ATP, 32P was incorporated into only two inositol phospholipids, i.e., tri- and diphosphoinositide (TPI and DPI). Even after the alkali treatment of the membrane, AChR-rich membranes still showed a considerable DPI kinase activity upon addition of exogenous DPI. It is likely that the 32P-incorporation into these lipids was realized by the membrane-bound DPI kinase and phosphatidyl inositol (PI) kinase. Such a membrane-bound DPI kinase was activated by Ca2+ (greater than 10(-6) M), whereas the PI kinase appeared to be inhibited by Ca2+. The effect of Ca2+ on the DPI phosphorylation was further enhanced by the addition of ubiquitous Ca2+-dependent regulator protein calmodulin. Calmodulin antagonists such as chlorpromazine (CPZ), trifluoperazine (TFP), and N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7) inhibited the phosphorylation of DPI in the AChR-rich membranes. It is suggested that the small pool of TPI in the plasma membrane is replenished by such Ca2+- and calmodulin-dependent DPI kinase responding to the change in the intracellular Ca2+ level.  相似文献   
175.
176.
Comparison was made between the effects of local irradiation of gamma rays, s. c. injection of cis-diamminedichloroplatinum (II) (CDDP), systemic hyperthermia and their combinations on the i. m. transplanted murine mastocytoma. Increase of the mean survival time (M. S. T.) by a factor of 1.72 and of 1.68 was achieved by a single irradiation at 20 Gy, given on day 5 after transplantation, and by injections of CDDP at 2 mg/kg, given s. c. on days 5 and 12 after transplantation, respectively. Increase of M. S. T. by a factor of 1.10 which was achieved with systemic hyperthermia of 41.8 degrees C of the core body temperature for 5 min, given twice, on days 5 and 12 after transplantation, was not statistically significant. The most effective one among all possible combinations within the 3 modalities was that of radiation and CDDP. Increase of M. S. T. was by a factor of 4.01.  相似文献   
177.
Acute and chronic effects of γ-butyrolactone-γ-carbonyl-histidyl-prolinamide (DN-1417) were investigated on motor activity, dopamine (DA) metabolites and DA receptors in various brain regions of rats. The motor activity, as measured with Automex recorder, was enhanced after a single injection with DN-1417 (20 mg/kg, IP), and the motor stimulating action persisted during 21 daily injections. Acute DN-1417 elevated both homovanillic acid (HVA) and 3,4-dihydroxyphenylacetic acid (DOPAC) levels in 7 brain regions, prefrontal cortex polar, medial and lateral fields, nucleus accumbens, olfactory tubercles, amygdala and striatum. After chronic treatment for 7 days, the acute effect of DN-1417 on DA metabolites disappeared in all regions except for the striatum in which DN-1417 still increased HVA and DOPAC. The response of striatal DA metabolites was also observed after chronic treatment for 21 days. Chronic DN-1417 produced no significant change in 3H-spiperone binding in the prefrontal cortex, nucleus accumbens, olfactory tubercles and striatum, while striatal 3H-DA binding displaced by 30 nM spiperone was enhanced after chronic treatment. These results indicate that DN-1417 interacts with mesocortical, mesolimbic and nigrostriatal DA systems in the different modes of action. The lack of tolerance to motor hyperactivity, however, raises the question as to whether DN-1417-induced hyperactivity may be mediated by the activation of mesolimbic DA neurons. The involvement of nigrostriatal neurons in DN-1417-induced motor hyperactivity is suggested.  相似文献   
178.
The complex of a bacterial alkaline serine proteinase, subtilisin BPN’, with its proteinaceous inhibitorStreptomyces subtilisin inhibitor is unique in several respects, compared with other similar complexes containing serine proteinases of trypsin family. In addition to the usual antiparallelβ-sheet involving P1-P3 residues of the inhibitor, P4-P6 residues form antiparallelβ-sheet with a previously unnoticed chain segment (the ‘S4-6 site’) of subtilisin. The ‘S4-6 site’ does not exist in serine proteinases of trypsin family, whether of mammalian or microbial origin. Global induced-fit movement seems to occur on the ‘trapped substrate’Streptomyces subtilisin inhibitor: a channel-like structure in SSI remote from the contact region becomes about 2 Å wider upon complexing with subtilisin. Main role of the secondary contact region ofStreptomyces subtilisin inhibitor seems to support the reactive site loop (primary contact region). Steric homology for the two contact regions is so high between the inhibitors ofStreptomyces subtilisin inhibitor family and those of pancreatic secretory trypsin inhibitor-ovomucoid inhibitor family that it seems to favour a divergent evolution and to support the general notion as to the relationship of prokaryotic and eukaryotic genes put forwarded by Doolittle(Nature (London),272, 581, 1978).  相似文献   
179.
180.
Net movements of water, Na, Cl, K, Ca, Mg and Pi were measured in the stripped and everted intestine of the carp. A high concentrative absorbtion of Pi was observed, whereas Na and Cl were absorbed almost isotonically. The rate of Pi absorption was greater in the middle part than in the anterior or posterior part of the intestine.  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