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   1689篇
  免费   177篇
  国内免费   1篇
  1867篇
  2022年   19篇
  2021年   29篇
  2020年   15篇
  2019年   17篇
  2018年   20篇
  2017年   26篇
  2016年   31篇
  2015年   67篇
  2014年   60篇
  2013年   67篇
  2012年   93篇
  2011年   78篇
  2010年   52篇
  2009年   55篇
  2008年   57篇
  2007年   74篇
  2006年   60篇
  2005年   45篇
  2004年   47篇
  2003年   48篇
  2002年   43篇
  2001年   48篇
  2000年   72篇
  1999年   36篇
  1998年   23篇
  1997年   28篇
  1996年   24篇
  1995年   22篇
  1994年   18篇
  1993年   22篇
  1992年   43篇
  1991年   40篇
  1990年   31篇
  1989年   31篇
  1988年   43篇
  1987年   27篇
  1986年   26篇
  1985年   30篇
  1984年   24篇
  1983年   20篇
  1982年   21篇
  1981年   11篇
  1980年   12篇
  1979年   16篇
  1978年   14篇
  1977年   13篇
  1976年   17篇
  1975年   12篇
  1974年   11篇
  1973年   19篇
排序方式: 共有1867条查询结果,搜索用时 0 毫秒
11.
A prospective study with mild general analgesia and sedation together with local anesthesia during bone marrow harvest was performed. Thirty-one patients underwent 33 bone marrow collections. Pretreatment consisted of 100 mg meperidine i.m. and 20 mg diazepam i.m. 1 h before start of procedure. Eight patients got additional meperidine and diazepam during the procedure, all patients got lidocaine 1% locally. A mean volume of 1.321 was obtained with 42.5 punctures. Twenty-two patients had no complications, 4 vomited, 4 had easily correctable hypotension of short duration, one got oxygen for cyanosis of short duration. Acceptance was good in 23 patients, in 6 reasonably well, in two bad. Only one patient experienced pain problems, due to suction. Anxiety was no major problem due to good information before the procedure and mild sedation. This form of anesthesia for bone marrow collection is a safe procedure, it is generally well accepted by the patient and it can be performed on an out-patient basis.  相似文献   
12.
13.
Summary Re-examination of the colorimetric fatty acid determination with copper nitrate, followed by complex formation with DIECA has shown that the method is not reliable if applied as described by Duncombe (1962, 1963): The Cu concentration is too high, the DIECA concentration much too low and the wavelength chosen (440 m) is suitable only for very low fatty acid concentrations.According to the results reported here the following alterations have to be adopted: The concentration of the copper nitrate solution should be 3%, a 0.5% solution of DIECA in butanol has to be used and measurements should be done at 492 m. The method described here offers the opportunity to determine fatty acid concentrations in the semi-micro range by measuring the filtered chloroform phase directly at 691 m, covering a range between 175 g/ml to 1.2 mg/ml. If the concentration turns out to be lower than 200 g F. A./ml, the same sample can be used for a micro-determination (up to 200 g/ml) at 492 m, after formation of the yellowish-brown complex by addition of 0.1 ml 0.5% butanolic DIECA solution to 1.0 ml of the chloroform phase.The method has been applied to determine the amount of free F. A. in cutin layers and cutin powder, revealing that the latter contains 5.6 times more free F. A. than the intact material. The free F. A. within the polymer seem to serve as interconnections for the main units of the cutin polylipid.  相似文献   
14.
Summary Zonae pellucidae of the viviparous goodeid teleosts Girardinichthys viviparus, Xenoophorus captivus, and Xenotoca eiseni were investigated ultrastructurally, and binding sites for ConA and WGA were localized on cross-sections using a colloidal gold technique. In late stages of development, the oocytes are surrounded by a three-zonated acellular matrix multiply perforated by pore canals allowing long microvilli of the oocyte to penetrate interstices of the follicle epithelium. Together, the surface of the microvilli and zona pellucida is coated by a thin layer of homogeneous slightly electron-dense material. In early oogenesis, the thin acellular layer is entirely packed with binding sites for WGA, whereas those for ConA occur only sparsely. Three-zonated zonae pellucidae amply contain both WGA and ConA receptors. The asymmetric labelling pattern obtained with both lectin protein gold preparations indicates a polarized organization of the different glycoconjugates. WGA receptors are concentrated within the outer region of the zona pellucida. Labelling with ConA-HRP-Au complexes produced heavy deposits of marker beads within the inner two thirds of the zona pellucida and weak labelling of the superficial coat. After prolonged digestion with neuraminidase, WGA binding sites were no longer detectable.Supported by the Deutsche Forschungsgemeinschaft (Schi 268/1-1)  相似文献   
15.
Campylobacter sputorum subspecies bubulus was grown in batch cultures in which the dissolved oxygen tension (d.o.t) was maintained at various constant levels. At a range of d.o.t. from 0.002 to 0.05 atm, which allowed good growth (mean generation time approximately 1.5 h), L-lactate was preferentially consumed before D-lactate. L-lactate oxidation was accompanied by equimolar acetate production during exponential growth. A value for YL-lactate (g dry weight bacteria per mol L-lactate) of 54 was determined. Net acetate production stopped when C. sputorum started to use D-lactate after consumption of L-lactate. When a culture growing exponentially at the expense of L-lactate was shifted from a d.o.t. of 0.02 atm to a d.o.t. of 0.15 atm, growth was impaired, and L-lactate consumption and corresponding acetate production diminished. This decrease correlated with a loss of lactate dehydrogenase activity after the shift. Campylobacter sputorum appeared to possess cytochromes of the b- and c-type and a carbon monoxide-binding pigment. Evidence is given that the principal site of oxygen damage is lactate dehydrogenase rather than the cytochrome chain.  相似文献   
16.
17.
The Steel factor.   总被引:1,自引:0,他引:1  
Steel factor (SLF) is a recently identified growth factor which is the gene product of the murine Steel locus and a ligand for the c-kit tyrosine kinase receptor, the product of the dominant white spotting locus (W). Defects at these genetic loci result in aberrant melanocyte, germ cell, and hematopoietic development. Both the receptor (c-kit) and the ligand (SLF) have been shown to undergo tissue-specific mRNA splicing to produce distinct isoforms which have unique biological functions. As predicted by the phenotype of these mutations, SLF influences the growth and differentiation of melanocytes, primordial germ cells, and a broad spectrum of cell types in the hematopoietic progenitor and stem cell hierarchy. SLF has also been shown to have effects on hematopoietic lineages not predicted by defects seen in the Steel mouse.  相似文献   
18.
We describe the combination of hot banding with fluorescence in situ hybridization as a rapid and efficient method to identify integration sites of transfected DNA sequences in chromosomes. As a test system we used SW480 EJ2, a clonal cell line obtained after transfection of SW480 with pSV2neoEJ, a plasmid containing a point-mutated, c-Ha-RAS oncogene. Nick-translated probes were compared with random primed-labeled probes to evaluate their relative efficiency in fluorescence in situ hybridization. The fluorescence signals were quantified in interphase nuclei by confocal scanning laser microscopy. Nick-translated probes were found to yield better results. Hot banding followed by fluorescence in situ hybridization localized the integration site of pSV2neoEJ in SW480 EJ2 at the site of a translocation on a marker chromosome Xp+. The combination of fluorescence in situ hybridization and hot banding can be used to (a) rapidly and efficiently analyze integration sites in large numbers of transfectants, (b) assess the clonality of transfected cell lines, and (c) localize the site of integration of transfected genes in the recipient genome.  相似文献   
19.
To study the role of T cells in T-B cell interactions resulting in isotype production, autologous purified human splenic B and T cells were cocultured in the presence of IL-2 and Con A. Under these conditions high amounts of IgM, IgG, and IgA were secreted. B cell help was provided by autologous CD4+ T cells whereas autologous CD8+ T cells were ineffective. Moreover, CD8+ T cells suppressed Ig production when added to B cells cocultured with CD4+ T cells. Autologous CD4+ T cells could be replaced by allogeneic activated TCR gamma delta,CD4+ or TCR alpha beta,CD4+ T cell clones with nonrelevant specificities, indicating that the TCR is not involved in these T-B cell interactions. In contrast, resting CD4+ T cell clones, activated CD8+, or TCR gamma delta,CD4-,CD8- T cell clones failed to induce IL-2-dependent Ig synthesis. CD4+ T-B cell interaction required cell-cell contact. Separation of the CD4+ T and B cells by semiporous membranes or replacement of the CD4+ T cells by their culture supernatants did not result in Ig synthesis. However, intact activated TCR alpha beta or TCR gamma delta,CD4+ T cell clones could be replaced by plasma membrane preparations of these cells. Ig synthesis was blocked by mAb against class II MHC and CD4. These data indicate that in addition to CD4 and class II MHC Ag a membrane-associated determinant expressed on both TCR alpha beta or TCR gamma delta,CD4+ T cells after activation is required for productive T-B cell interactions resulting in Ig synthesis. Ig production was also blocked by mAb against IL-2 and the IL-2R molecules Tac and p75 but not by anti-IL-4 or anti-IL-5 mAb. The CD4+ T cell clones and IL-2 stimulated surface IgM-IgG+ and IgM-IgA+, but not IgM+IgG- or IgM+IgA- B cells to secrete IgG and IgA, respectively, indicating that they induced a selective expansion of IgG- and IgA-committed B cells rather than isotype switching in Ig noncommitted B cells. Induction of Ig production by CD4+ T cell clones and IL-2 was modulated by other cytokines. IL-5 and transforming growth factor-beta enhanced, or blocked, respectively, the production of all isotypes in a dose-dependent fashion. Interestingly, IL-4 specifically blocked IgA production in this culture system, indicating that IL-4 inhibits only antibody production by IgA-committed B cells.  相似文献   
20.
The death receptor CD95 (APO-1/Fas), the anticancer drug etoposide, and gamma-radiation induce apoptosis in the human T cell line Jurkat. Variant clones selected for resistance to CD95-induced apoptosis proved cross-resistant to etoposide- and radiation-induced apoptosis, suggesting that the apoptosis pathways induced by these distinct stimuli have critical component(s) in common. The pathways do not converge at the level of CD95 ligation or caspase-8 signaling. Whereas caspase-8 function was required for CD95-mediated cytochrome c release, effector caspase activation, and apoptosis, these responses were unaffected in etoposide-treated and irradiated cells when caspase-8 was inhibited by FLIPL. Both effector caspase processing and cytochrome c release were inhibited in the resistant variant cells as well as in Bcl-2 transfectants, suggesting that, in Jurkat cells, the apoptosis signaling pathways activated by CD95, etoposide, and gamma-radiation are under common mitochondrial control. All three stimuli induced ceramide production in wild-type cells, but not in resistant variant cells. Exogenous ceramide bypassed apoptosis resistance in the variant cells, but not in Bcl-2-transfected cells, suggesting that apoptosis signaling induced by CD95, etoposide, and gamma-radiation is subject to common regulation at a level different from that targeted by Bcl-2.  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