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   4900篇
  免费   336篇
  国内免费   1篇
  2023年   38篇
  2022年   40篇
  2021年   136篇
  2020年   96篇
  2019年   106篇
  2018年   138篇
  2017年   113篇
  2016年   178篇
  2015年   236篇
  2014年   285篇
  2013年   320篇
  2012年   382篇
  2011年   350篇
  2010年   224篇
  2009年   174篇
  2008年   259篇
  2007年   237篇
  2006年   214篇
  2005年   195篇
  2004年   159篇
  2003年   189篇
  2002年   166篇
  2001年   72篇
  2000年   69篇
  1999年   66篇
  1998年   54篇
  1997年   36篇
  1996年   45篇
  1995年   40篇
  1994年   38篇
  1993年   44篇
  1992年   48篇
  1991年   36篇
  1990年   34篇
  1989年   35篇
  1988年   22篇
  1987年   24篇
  1986年   15篇
  1985年   33篇
  1984年   30篇
  1983年   19篇
  1982年   30篇
  1981年   18篇
  1980年   24篇
  1979年   30篇
  1978年   13篇
  1977年   16篇
  1976年   15篇
  1974年   15篇
  1973年   13篇
排序方式: 共有5237条查询结果,搜索用时 125 毫秒
31.
Five brain-derived and 17 urinary oligomannose-type oligosaccharides were isolated by ion-exchange chromatography on Mono Q or Dowex, followed by HPLC on Lichrosorb-NH2 from a Persian cat suffering from -mannosidosis. The structures ofthe carbohydrate chains were determined by 500- or 600-MHz1H-NMR spectroscopy. Different oligosaccharide patterns were found in brain and urine. 99% of the urinary oligosaccharides possess an (1-6)-linked mannose residue attached to -mannose, whereas only 5% of the brain-derived oligosaccharides contain such a residue. Furthermore, of the urinary carbohydrate chains 71% end with Man1-4GlcNAc1-4GlcNAc and 29% end with Man1-4GlcNAc, whereas the corresponding amounts are 23% and 77%, respectively, for the brain-derived oligosaccharides.Abbreviations MLEV-17 composite pulse devised by M. Levitt - HOHAHA homonuclear Hartman-Hahn spectroscopy - TPPI time-proportional phase incrementation - 2D two dimensional - GlcNAc N-acetylglucosamine - Man mannose - Fuc fucose  相似文献   
32.
Summary The purpose of this phase I study was to evaluate the toxicity and biological activity of autologous blood-derived macrophages activated ex-vivo with recombinant human interferon (rhuIFN) [monokine-activated killer (MAK) cells] and administered intravenously to 11 lung cancer patients once a week for 6 consecutive weeks. Peripheral blood monocytes were collected by leukapheresis and then purified by counterflow elutriation. The MAK cells were generated by culturing the purified monocytes in Teflon bags for 7 days and adding rhuIFN to the cultured cells for the last 18 h. These MAK cells expressed differentiation-associated surface antigen MAX1, and were cytotoxic in vitro against tumour cell line U937. The MAK cells were infused at dose levels from 1 × 107 to 5 × 108 on an intrapatient dose-escalating schedule. No severe adverse side-effects occurred. Toxicity was mild to moderate [primarly fever (75%) and chills (32%)], non-dose-dependent, and non-cumulative. No consistent change in haemostatic function, or liver or renal function was observed. Dose-limiting toxicity was not reached at 5 × 108 cells (optimal dose reproduced for each patient). The maximum tolerated dose was not determined. The immunomodulatory activity of i.v. infused MAK cells was demonstrated both in vivo by significant increases in granulocyte count and neopterin level in the patients' peripheral blood postinfusion and in vitro by secretory products (IL-1. TNF, neopterin, and thromboplastin-like substance) in the culture supernatants. The in vivo traffic patterns of autologous MAK cells labelled ex-vivo with111In oxine were studied in 7 patients. Gamma imaging showed an immediate but transient lung uptake (<24 h), and a progressive uptake of radioactivity in the liver and spleen was seen from 6 h to 72 h post-infusion. Our results indicate that the preparation of high numbers of autologous, blood-derived MAK cells is a feasible procedure, and their transfusion is safe for patients. This immunotherapeutic approach seems to be encouraging from the point of view of establishing an adjuvant therapeutic modality in cancer patients with minimal residual disease.This work was supported in part by a grant 6911 from the Association pour la Recherche contre le Cancer (ARC), grants from the Ligue Nationale contre le cancer and the Ligues Regionales (Bas-Rhin, Haut-Rhin) contre le cancer, and contract 891013 from the Institut National pour la Santé et la Recherche Médicale (INSERM), France  相似文献   
33.
A one-step clearing and embedding procedure for alizarin red S stained skeletons is described. Embryos are fixed in formalin, skinned and eviscerated. After staining in a 10 mg/liter solution of alizarin red S in 5% aqueous KOH, specimens are dehydrated in a graded series of acetone-polyester monomer solutions. Finally, the specimens are embedded at room temperature in the polyester resin. A special reusable metallic mold is described for embedment of large fetuses. Specimens previously cleared in glycerol can be processed with this method.  相似文献   
34.
Mitotic activity and nuclear DNA synthesis in tomato ( Lycopersicon esculentum Mill., cv. King plus) flowers targeted for abortion under unfavorable light conditions are completely stopped 6 days after macroscopic appearance of the inflorescence. Ovular cells are arrested at the G1 (80%) and G2 (20%) stages of the cell cycle. Exogenous applications of a mixture of N6-benzyladenine (BA) and gibberellins A4+7 (GA) directly on the inflorescence may prevent its failure. Nuclear DNA synthesis and mitoses resume in ovules of the flower 16 to 20 h after the BA+GA treatment. When applied alone, BA and GA are able to mimic the effect of the mixture upon the progression of ovular cells through their cycle. Sporogenesis processes are also set in motion by the exogenous plant growth regulators. The mechanism of action of cytokinins and gibberellins in the control of floral development is discussed.  相似文献   
35.
36.
Summary Detergent insoluble material (DIM) was prepared by gentle treatment with detergent from foetal, regenerating and adult normal rat hepatocytes cultured for various times. It retained to some degree the morphology of the cells. After incubation of intact cells with 35S-methionine, most of the labelled DIM proteins were found to be components of the cytoskeleton. They included several cytokeratins, vimentin and actin. The synthesis rate varied with the age of animals and culture conditions. The high synthetic rate of vimentin in foetal and regenerating hepatocytes could be associated with cell proliferation. No correlation was found between cytokeratin synthesis and hepatocyte growth. Most of the cytoskeleton proteins could be phosphorylated in intact cells and in DIM from cultured hepatocytes. However the degree of phosphorylation of these proteins was not related to their synthetic rate. The decreased phosphorylation level in cultured adult rat hepatocytes could be related to the rapid loss of specific functions.  相似文献   
37.
Two computation methods are explained; theirobject is the estimation of the velocity of animals which are known by their footprints, and in the case of the first method, by their skeletons as well.The first method is based on the compound pendulum theory, because during the slow walking gait, the motion of the leg is similar to the oscillation of a pendulum, for the computation of the velocity (v), are considered: moment of inertia (I), radius of gyration (P) and period (T), time in seconds to cover one stride (E) in the case the maximum angle of divarication (δ) of the leg with the vertical is ≤20°. A comparison with the formula of Alexander (1976) is discussed.The second method concerns saltator animals. It is based on the fondamental laws of dynamics. With the length of the jump (E) it is possible to estimate the velocity of the trackmaker (v) and the height of the jump (K). For the vertebrates the angle of the trajectory with the horizontal plan (α) is between 20 and 45°. Thus, the result of this method is an interval of estimation in which the velocity is included.These methods do not give precise results. But these approximations supply valid informations on the velocity of extinct or living animals and can lead to the estimation of their maximum speed if the parameters E, T, vary. The problem of the errors is also discussed. It is shown that the errors in estimating the parameters have a no significant influence on the results.  相似文献   
38.
An aminopeptidase from human urine (HUA) able to hydrolyze L-aminoacyl-2-naphthylamides, L-Leu-p-nitroanilide and to convert both MLBK and LBK to BK has been further purified and characterized. The preparation now obtained showed a 3-fold higher specific activity than the previously described one and a single active protein band in 7% polyacrylamide gel electrophoresis accounting for 86% of total protein. Kinetic constants for this kinin-converting enzyme were determined using L-aminoacyl-2-naphthylamides, L-Leu-p-nitroanilide and LBK. The Km values for different naphthylamides were in the 10(-5) M range while that for L-Leu-p-nitroanilide was 3.6 X 10(-4) M. With LBK as substrate the aminopeptidase activity showed the highest catalytic efficiency in spite of a Km in the mM range. The enzyme was poorly inhibited by -SH and -S-S- group reagents. Some L-aminoacids, as well as mono- and diamines, indomethacin, puromycin and bestatin were equipotent competitive inhibitors of both arylamidase and aminopeptidase activities. Results obtained in this paper are compatible with our conclusion that human urine, unlike other enzyme sources, contains only one aminopeptidase, and that this enzyme displays both arylamidase and kinin-converting activities. The enzyme's action may be important in the metabolism of kinins, yielding peptides which could interact with both B-1 and B-2 kinin receptors in the kidney.  相似文献   
39.
40.
The immunogenicity and reactogenicity of the Urabe Am 9 mumps virus vaccine strain were studied after the administration of different doses of the vaccine to 197 children ranging in age from seven and a half months to nine years and without a history of mumps. There was no effect of dose on the response in serum neutralizing antibodies in the range of 10(2.9) to 10(4.7) TCID50/dose. In the 90 subjects without detectable serum neutralization antibodies before vaccination seroconversion was obtained in 94.4% after 42 days. Half of a group of 34 seropositive children who were tested also showed a fourfold or greater rise in antibodies. Persistence of vaccine-enhanced haemagluttinin-inhibition (EHI) antibodies was satisfactory as only two of 46 vaccinees followed-up for between 27 and 32 months had undetectable levels of EHI antibodies and the geometric mean titre of vaccine-induced EHI antibodies had only fallen to about one-third by 32 months after vaccination. Although there was serological evidence of a subclinical re-infection in three subjects, to date none of the vaccinees has had clinical mumps indicating that the vaccine confers protection against disease. The vaccine was well tolerated. Furthermore, the majority of the few 'reactions' reported were probably not vaccine-related. It is concluded that the Urabe Am 9 is an acceptable strain for use in live mumps vaccines.  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