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   655篇
  免费   32篇
  国内免费   1篇
  2021年   2篇
  2020年   3篇
  2018年   11篇
  2017年   6篇
  2016年   6篇
  2015年   13篇
  2014年   20篇
  2013年   54篇
  2012年   33篇
  2011年   45篇
  2010年   27篇
  2009年   20篇
  2008年   35篇
  2007年   44篇
  2006年   42篇
  2005年   41篇
  2004年   48篇
  2003年   41篇
  2002年   31篇
  2001年   10篇
  2000年   11篇
  1999年   7篇
  1998年   13篇
  1997年   8篇
  1996年   5篇
  1995年   5篇
  1994年   3篇
  1993年   5篇
  1992年   11篇
  1991年   7篇
  1990年   7篇
  1989年   4篇
  1988年   6篇
  1987年   3篇
  1986年   4篇
  1985年   6篇
  1984年   8篇
  1983年   7篇
  1982年   5篇
  1981年   2篇
  1980年   5篇
  1978年   1篇
  1977年   3篇
  1976年   3篇
  1975年   3篇
  1974年   3篇
  1972年   2篇
  1971年   3篇
  1967年   2篇
  1957年   1篇
排序方式: 共有688条查询结果,搜索用时 15 毫秒
11.
Summary Maximum production of alkaline serine protease by Bacillus alcalophilus subsp. halodurans KP 1239 was achieved after 24 h cultivation, at an initial pH of 7.6, on a medium containing 1.0% sodium citrate, 0.3% yeast extract, and 0.3% KH2PO4. The enzyme was purified to crystalline form from culture broth. The enzyme was most active at 60° C and at pH 11.5. The molecular weight, isoelectric point and sedimentation coefficient in water at 20° C were estimated as 29 000, 8.8 and 3.3S, respectively. The N-terminal amino acid sequence was Ala-Gln-Ser-Val-Pro-Trp-Gly-Ile-Ser-Arg-Val-Gln-Ala-Pro-Ala-Ala-His-Asn-Arg-Gly-. The enzyme shared its antigenic determinants with B. alcalophilus ATCC 21522 serine protease, but not with the subtilisins Carlsberg and BPN. Offprint requests to: Yuzuru Suzuki  相似文献   
12.
Growth of chimpanzees reared at the Kumamoto Primates Park of Sanwa Kagaku Kenkyusho Co. Ltd. was studied cross-sectionally from the viewpoints of somatic growth and reproductive maturation. Distance and velocity curves were expressed using spline function method. Males showed adolescent growth acceleration in body weight, with a peak at 7.86 yrs of age, but not in trunk length. Females showed continuous rapid growth from mid-juvenile to adolescent phase in both body weight and trunk length, but no isolated adolescent spurt. The Sanwa chimpanzees matured at about 12.5 yrs of age for females and 15.0 yrs for males. The mean adult weights and trunk lengths were 53.2 kg and 507.8 mm for males and 42.7 kg and 481.6 mm for females. The Sanwa chimpanzees had similar growth patterns to those of the Yerkes chimpanzees, although they showed a slight delay in infancy, and a higher growth rate from the early juvenile phase onwards. Growth patterns in these two laboratories may be regarded as “normative” for laboratory-reared chimpanzees. They matured earlier than wild chimpanzees by more than two years. The major reason for the retarded maturation in wild chimpanzees is the delay of growth from infant to the early juvenile phases (0–4 yrs of age), probably owing to a limited nutritional supply from the mother. Development of the testes comprised three phases: slow growth from infant to juvenile (until 6.4 yrs); rapid growth around adolescence (until 9.2 yrs); and adult (mean testicular volume, 187 cm3). Setting the nutritional standard at 2,000–2,600 Cal/day (= Kcal/day) per adult, calories were considered for captive chimpanzees in each age class.  相似文献   
13.
Abstract: 6R-l -erythro-Tetrahydrobiopterin (6R-BH4) is a cofactor for aromatic l -amino acid hydroxylases and nitric oxide synthase. Recently, we have reported that independently of its cofactor activities, 6R-BH4 acts from the outside of neurons in the brain to enhance the release of monoamine neurotransmitters such as dopamine. To characterize the pharmacological properties of the action, we examined the effects of 6S-BH4, a diastereoisomer of 6R-BH4, on dopamine release in the rat striatum by using brain microdialysis and compared its effects with those of 6R-BH4. Perfusion of 6S-BH4 or 6R-BH4 through the dialysis probe increased extracellular dopamine levels (an index of in vivo dopamine release) concentration dependently; the maximal increase by 6S-BH4, was one-sixth of that by 6R-BH4. 6S-BH4 increased extracellular DOPA levels in the presence of NSD 1015, an inhibitor of aromatic l -amino acid decarboxylase (an index of in vivo tyrosine hydroxylase activity), to an extent similar to the increase induced by 6R-BH4. The increase in the DOPA levels induced by either of the pteridines was abolished after pretreatment of rats with α-methyl-p-tyrosine (an inhibitor of tyrosine hydroxylase). Under the same conditions, the 6S-BH4-induced dopamine release was abolished, but most of the 6R-BH4-induced increase persisted. Coadministration of 6S-BH4 with 6R-BH4 inhibited the increase in dopamine release induced by 6R-BH4 alone. These results show that 6R-BH4 stimulates dopamine release by acting at the specific recognition site on the neuronal membrane, and that 6S-BH4 acts as an antagonist of 6R-BH4 at this site, although it has cofactor activities.  相似文献   
14.
We have recently shown that differentiation-inducing factor-1 (DIF-1) of Dictyostelium discoideum is capable of raising intracellular calcium concentration ([Ca2+]i) and suppressing cell proliferation of rat pancreatic AR42J cells in a dose-dependent manner, and that DIF-1 at a concentration of 40 μmol/L is toxic to the cells. In this study, we have further characterized the cytotoxic effect of DIF-1 on AR42J cells and have analyzed the effect of DIF-1 on [Ca2+]i. In the presence of 40 μmol/L DIF-1, cells began to bleb after approximately 6 h, and most had died within 48 h. Biochemical analysis revealed that DNA fragmentation was accompanied by cell death. Monitoring the changes in [Ca2+]i induced by DIF-1, it was found that cells were able to adapt to stimulation with DIF-1 so that they did not respond to subsequent stimulation by DIF-1. These results indicate that DIF-1 induced apoptosis in AR42J cells probably via a cell signaling system.  相似文献   
15.
In previous ultrastructural studies we have shown that at the tip of intestinal villi in guinea pigs, effete enterocytes are separated into two portions: a thin apical cytoplasm to be exfoliated into the lumen and a major basal portion to be ingested by lamina propria macrophages. During this process, intraepithelially disposed, large granular lymphocytes interdigitate with enterocytes in a complex manner. In the present study, the relation between the enterocytes and the lymphocytes in the villous epithelium of the guinea pig small intestine is described by use of transmission and scanning electron microscopy in an attempt to visualize the roles and activities of the lymphocytes more clearly. The lymphocytes project numerous pointed processes into effete enterocytes, even piercing them. Enterocytes are deeply indented or perforated, probably as a result of the encroaching lymphocyte processes. Some enterocytes are separated into apical and basal portions by numerous large excavations in the cytoplasm. These findings indicate that repeated perforating penetration of the lymphocytes induces cell cleavage. Supporting this supposition, our microcinematographic observations demonstrate the alternate protrusion and withdrawal of processes of lymphocytes. The processes advance with a pointed end, and subsequently, retract with a rounded end in a cycle of 8–18 seconds.  相似文献   
16.
Summary The usefulness of LMS in postoperative immunochemotherapy of gastric cancer was investigated. In compliance with the protocol, MMC was given at a dose of 20 mg on the day of gastrectomy, and an additional 10 mg on the next day IV. The patients receiving 600 mg Tegafur daily were then divided into two groups according to whether LMS was also given or not. LMS was administered for 3 days before the operation in a daily dose of 150 mg and for 1 year or more after operation according to a schedule of 3 days' administration followed by an 11-day interval. The 2-year follow-up demonstrated that in stage III patients, the LMS (+) regimen was superior to the LMS (–) regimen, since the former prolonged the relapse-free interval significantly. The survival rate for stage III disease was also significantly higher in the LMS (+) than in the LMS (–) group. There was no significant difference in the incidence of subjective or objective side-effects between two groups. The incidence of agranulocytosis was comparable in the two groups.Gastrointestinal Cancer Research Group, Japan Levamisole Research AssociationChairmen of the Gastrointestinal Cancer Research Group, Japan LMS Research AssociationController of the Gastrointestinal Cancer Research Group, Japan LMS Research AssociationMembers of the Data Collection and Analysis SubcommitteeThis study was carried out by the Gastrointestinal Cancer Research Group, Japan LMS Research Association (directed by Prof. Kiyoshi Inokuchi, Dept. of Surgery, Kyushu University and Prof. Eiro Tsubura, Dept. of Internal Medicine, Tokushima University). The results were presented in part at the 19th General Meeting of the Japanese Society for Gastroenterological Surgery in February, 1982  相似文献   
17.
Total phospholipids were extracted from cells of temperature sensitive unsaturated fatty acid auxotrophs of Escherichia coli (K-12 UFAts) grown at 28°C (PL28), and at 42°C in the presence of 2% KCl as an osmotic stabilizer (PL42 (KCl)). From the analysis of fatty acids, it was shown that the content of unsaturated fatty acids of PL42 (KCl) is only 9% of the total fatty acids, while that of PL28 is 54%. The thermal phase transitions of the bilayers prepared from the phospholipid fractions were studied by proton magnetic resonance. The line widths of the methylene signals and the sums of the methylene and methyl signal intensities were plotted against reciprocal values of absolute temperature 1/T or temperature itself. From the plots phase transitions were detected at about 19°C for PL28 and at 43°C for PL42 (KCl). In spite of its complex composition of fatty acids a highly cooperative transition was observed in the case of PL42 (KCl). It was also suggested that the phospholipids bilayers in the biomembranes of this strain at the growth temperature (42°C) are in the state where the gel and liquid crystalline phases coexist.  相似文献   
18.
Summary A fumaric acid-assimilating obligate thermophile having a high aspartase activity was isolated from soil. The isolate (KP 1041) that grew at 45 to 68 °C was assigned to a strain of Bacillus stearothermophilus. The cell suspensions produced L-aspartate from fumarate and ammonium ion, with the rapidest initial rate at 65 °C and pH 9.5. The Michaelis constant for fumarate was 0.2 M. The cellular aspartase was relatively stable for 18 h at and below 50 °C over a pH range 6.7–8.3 in the presence of ammonium fumarate; this substance protected the enzyme from heat inactivation. The best yield in L-aspartic acid production was achieved at 6 h incubation at 53 °C and pH 8.5, using 0.88 M fumarate, 3.1 M ammonium ion, and the cells at 53 mg dry weight per ml. In this case, 85% of fumarate added was converted into aspartic acid. The structure of the product was determined from its infrared spectrum, specific rotation, melting point and ultimate analysis.Presented at the Annual Meeting of the Agricultural Chemical Society of Japan, Yokohama, April 2, 1977  相似文献   
19.
20.
We have generated a number of mAb against various epitopes on the external envelope glycoprotein, gp46, of human T cell leukemia virus type I (HTLV-I) from a WKA rat immunized with a recombinant vaccinia virus containing the HTLV-I env gene. Among these mAb, one group of mAb, represented by a mAb designated LAT-27, could neutralize the infectivity of HTLV-I, as determined by a HTLV-I-mediated cell fusion inhibition assay. LAT-27 also interfered with transformation of normal T lymphocytes by HTLV-I in vitro. An antibody-binding assay using overlapping synthetic oligopeptides showed that LAT-27 bound specifically to 10-mer peptides that contained the gp46 amino acid sequence 191-196 (Leu-Pro-His-Ser-Asn-Leu). Antibodies from HTLV-I+ humans interfered with the binding of LAT-27 to gp46 Ag. Sera from rabbits immunized with a LAT-27-reactive peptide, 190-199, conjugated with OVA, but not sera from OVA-immunized rabbits, reacted with gp46 Ag and neutralized infectivity of HTLV-I. These results show that the HTLV-I neutralization epitope recognized by LAT-27 locates to the gp46 amino acids 191-196, and that immunization with a peptide containing the LAT-27 epitope can elicit an HTLV-I neutralizing antibody response.  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