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   627篇
  免费   64篇
  国内免费   1篇
  692篇
  2024年   1篇
  2023年   5篇
  2022年   11篇
  2021年   20篇
  2020年   12篇
  2019年   18篇
  2018年   19篇
  2017年   16篇
  2016年   15篇
  2015年   49篇
  2014年   52篇
  2013年   33篇
  2012年   53篇
  2011年   42篇
  2010年   32篇
  2009年   24篇
  2008年   37篇
  2007年   27篇
  2006年   33篇
  2005年   43篇
  2004年   34篇
  2003年   23篇
  2002年   20篇
  2001年   11篇
  2000年   6篇
  1999年   10篇
  1998年   4篇
  1997年   3篇
  1996年   7篇
  1994年   2篇
  1993年   1篇
  1992年   2篇
  1990年   1篇
  1988年   1篇
  1987年   4篇
  1986年   1篇
  1985年   2篇
  1984年   1篇
  1983年   2篇
  1982年   1篇
  1981年   2篇
  1979年   4篇
  1978年   1篇
  1977年   2篇
  1976年   2篇
  1972年   2篇
  1968年   1篇
排序方式: 共有692条查询结果,搜索用时 15 毫秒
681.
  1. Neochetina eichhorniae is the most widely established biocontrol agent on water hyacinth populations around South Africa. However, some N. eichhorniae populations have failed to adequately control their host population, specifically those exposed to cold conditions.
  2. The aim of this study was to determine whether two climatically distinct populations of N. eichhorniae in South Africa differ in their low‐temperature physiology, which tests whether local‐climate adaptation has occurred.
  3. We estimated weevil CTmin, LLT50, SCP, and SCP mortality using standard approaches. Contrary to expectation based on climatic thermal profiles at the two sites, weevils from the warm locality ((mean ± SE) CTmin = 5.0 °C ± 0.2, LLT50 = ?11.3 °C ± 0.03, SCP = ?15.8 °C ± 0.6) were able to maintain activity and tolerate colder temperatures than the weevils from the colder site (CTmin = 6.0 °C ± 0.5, LLT50 = ?10.1 °C ± 0.1, SCP = ?12.9 °C ± 0.8).
  4. These contradictory outcomes are likely explained by the poor nutrient quality of the plants at the cold site, driving low‐temperature performance variation that overrode any macroclimate variation among sites. The cold site weevils may also have adapted to survive wide‐temperature variability, rather than perform well under very cold conditions. In contrast, the mass‐reared population of insects from the warm site has likely adapted to the consistent conditions that they experience over many years in confinement.
  相似文献   
682.
ATP, ADP, and adenosine have been found to inhibit acetylcholine-stimulated secretion from isolated cells of bovine adrenal medulla (chromaffin cells). Maximal inhibition is approximately 30% under the conditions studied; half-maximal inhibition occurs at nucleotide concentration in the micromolar range. Cells must be incubated with ATP for approximately 90 s for maximal inhibition, but inhibition by adenosine occurs much faster, an observation suggesting the possibility that ATP and ADP exert their effect after being converted to adenosine. Experiments with cells preloaded with the fluorescent calcium chelator quin 2 indicate that external ATP can diminish the rise in cytosolic Ca2+ concentration that follows stimulation by acetylcholine.  相似文献   
683.
684.
685.
Systematic modification of amino acid at position Y-2 of a library-derived non-phosporylated thioether-cyclized peptide, cyclo(CH2CO-Glu2-Leu-Tyr0-Glu-Asn-Val-Gly-Met-Tyr-Cys) -amide, aided by molecular modeling, demonstrates that the Glu(-2) sidechain compensates for the absence of Tyr0 phosphorylation in retaining effective binding to Grb2-SH2 domain. Replacement of Glu(-2) with gamma-carboxyglutamic acid produced a high affinity inhibitor, the first example with submicromolar affinity (IC50 = 640 nM).  相似文献   
686.
Summary Urogenital morphogenesis and cytodifferentiation are presented in the context of the epithelial-stromal interaction. The essential role of stroma in these processes is reviewed. Presented in the formal symposium on Sexual Differentiation in Vitro and in Vivo at the 29th Annual Meeting of the Tissue Culture Association, Denver, Colorado, June 4–8, 1978. The study was supported in part by Grant No. PDT-8 from the American Cancer Society, and Contract Grants N01-CP-55649 and N01-CP-75875 from the National Cancer Institute.  相似文献   
687.
Alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH) exhibit genetic polymorphism and tissue specificity. ADH and ALDH isozyme phenotypes from 39 surgical Chinese lung specimens were identified by agarose isoelectric focusing. The identity of the lung β-ADHs was further demonstrated by their characteristic pH-activity profiles for ethanol oxidation,K m values for NAD and ethanol, and inhibition by 4-methylpyrazole or 1,10-phenanthroline. The β2 allele, coding for β2 polypeptide, was found to be predominant in the lung specimens studied. The ADH activities in the lungs with the homozygous phenotype ADH2 2-2 (exhibiting β2β2) and ADH2 1-1 (exhibiting β1β1) and the heterozygous phenotype ADH2 2-1 (exhibiting β2β2, β2β1, and β1β1) were determined to be 999±77, 48±17, and 494±61 nmol/min/g tissue, respectively. Fifty-one percent of the specimens studied lacked the ALDH2 activity band on the isoelectric focusing gels. The activities in the lung tissues with the ALDH2-active phenotype and the inactive phenotype were determined to be 30±3 and 17±1 nmol/min/g tissue, respectively. These findings indicate that human pulmonary ethanol-metabolizing activities differ significantly with respect to genetic polymorphism at both theADH 2 and theALDH 2 loci. The results suggest that individuals with highV max β2-ADH and deficient in low-K m mitochondrial ALDH2, accounting for approximately 45% of the Chinese population, may end up with acetaldehyde accumulation during alcohol consumption, rendering them vulnerable to tissue injury caused by this highly reactive and toxic metabolite. This work was supported by Grants NSC 77-0412-B016-58 and NSC 80-0412-B016-21 from the National Science Council, Republic of China.  相似文献   
688.
Summary Immunological data were obtained during the course of a randomized trial comparing intrapleural BCG plus oral isoniazid (INH) with intrapleural saline plus oral placebo after resection of stage I non-small cell lung cancer. Immunological testing with a variety of assays was carried out with good standardization among six collaborating laboratories and with good reproducibility within each laboratory. Those patients with larger tumors tended to have higher initial white cell counts. The percentage of lymphocytes in the differential was greatest in those with non-squamous cancer histology. Otherwise, no associations were found between initial immunologic parameters and baseline variables. The main effect of BCG/INH therapy was to cause statistically significant increases in purified protein derivative (PPD) skin test induration and PPD in vitro blastogenesis compared with controls. Other skin tests and in vitro assays increased more in the saline/placebo control group, but these treatment differences were usually not statistically significant. Initial white count and neutrophil count elevations were found to be associated with increased risk of recurrence. Even after adjustment for treatment and tumor stage, initial neutrophil count elevation was associated with increased risk of recurrence. Surprisingly, a low 29° C T cell rosette index was associated with a decreased risk of recurrence, though the differences were minimal. Serial immunological tests were carried out to evaluate their potential for monitoring disease recurrence. White count elevations continued to be significantly associated with increased risk of recurrence, but more follow-up data are needed before other associations can be assessed.Members of the Lung Cancer Study Group include: E. C. Holmes** (Group Chairman), W. F. Coulson, K. P. Ramming, and T. H. Weisenburger from the University of California, Los Angeles; Z. Petrovich from Wadsworth Veterans Hospital, Los Angeles; R. T. Eagan**, R. E. Lee, W. S. Payne, R. E. Ritts, and L. Weiland from the Mayo Clinic, Rochester; C. F. Mountain**, H. T. Barkley, O. H. Frazier, K. Hermes, E. Hersh, and M. Valdivieso from the University of Texas System Cancer Center, MD Anderson Hospital, Houston; L. D. Hill**, M. D. Hafermann, and E. Morgan from the Mason Clinic, Seattle; P. W. Wright**, and K. E. Hellstrom from the Hutchinson Cancer Center, Seattle; C. Bagley, L. P. Johnson, H. Kellogg, and R. D. Pinkman from the Swedish Medical Center, Seattle; T. D. Ivey from University Hospital, Seattle; S. Hammar from Virginia Mason Hospital, Seattle; W. Nelems from St Paul's Hospital, Vancouver; R. Feld**, D. Bergsagel, T. C. Brown, J. Curtis, C. Keen, J. F. Pringle, I. Quirt, and L. Yeod from the Princess Margaret Hospital, Toronto; M. Blackstein and M. Goldberg from Mount Sinai Hospital, Toronto; F. G. Pearson**, D. W. Chamberlain, J. Cooper, W. Evans, and T. Todd from Toronto General Hospital, Toronto; M. Baker and R. Ginsberg from Toronto Western Hospital, Toronto; R. I. Mitchell from Wellesley Hospital, Toronto; R. K. Oldham**, J. T. Forbes, F. A. Greco, D. L. Page, R. Prager, R. L. Richardson, and S. L. Stroup from Vanderbilt University, Nashville; J. M. Lukeman** and S. M. Sajjad from the Pathology Reference Center of UT MD Anderson Hospital, Houston; P. Grifone, A. Lebeck, A. Sharpe, and T. Voss from the Operations Office, Silver Spring, Maryland; M. Gail and L. Rubinstein, Group Statisticians, W. McGuire, J. Allegra, G. Witman, Project Officers, from the National Cancer Institute, Bethesda, Maryland; and W. Heineman, J. Beach, L. Close, and B. Sharkey from Information Services, Bethesda, Maryland. Asterisks designate principal investigators  相似文献   
689.
The pulmonary vasoconstrictor, thromboxane, may contribute to the development of pulmonary hypertension. Our objective was to determine whether a combined thromboxane synthase inhibitor-receptor antagonist, terbogrel, prevents pulmonary hypertension and the development of aberrant pulmonary arterial responses in newborn piglets exposed to 3 days of hypoxia. Piglets were maintained in room air (control) or 11% O(2) (hypoxic) for 3 days. Some hypoxic piglets received terbogrel (10 mg/kg po bid). Pulmonary arterial pressure, pulmonary wedge pressure, and cardiac output were measured in anesthetized animals. A cannulated artery technique was used to measure responses to acetylcholine. Pulmonary vascular resistance for terbogrel-treated hypoxic piglets was almost one-half the value of untreated hypoxic piglets but remained greater than values for control piglets. Dilation to acetylcholine in preconstricted pulmonary arteries was greater for terbogrel-treated hypoxic than for untreated hypoxic piglets, but it was less for pulmonary arteries from both groups of hypoxic piglets than for control piglets. Terbogrel may ameliorate pulmonary artery dysfunction and attenuate the development of chronic hypoxia-induced pulmonary hypertension in newborns.  相似文献   
690.
In recent years, new treatment for renal cell carcinoma (RCC) has been a spotlight in the field of cancer therapeutics. With several emerging agents branded as 'targeted therapy' now available, both medical oncologists and urologists are progressively more hopeful for better outcomes. The new remedies may provide patients with improved survival and at the same time less toxicity when compared to traditional cytotoxic agents. This article will center on current and emerging treatment strategies for advanced RCC and other GU malignancies with updates from 2008 annual ASCO meeting.  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