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   867篇
  免费   77篇
  944篇
  2022年   8篇
  2021年   15篇
  2020年   17篇
  2019年   8篇
  2018年   16篇
  2017年   20篇
  2016年   11篇
  2015年   37篇
  2014年   39篇
  2013年   48篇
  2012年   39篇
  2011年   36篇
  2010年   38篇
  2009年   26篇
  2008年   37篇
  2007年   41篇
  2006年   35篇
  2005年   20篇
  2004年   25篇
  2003年   30篇
  2002年   26篇
  2001年   35篇
  2000年   26篇
  1999年   23篇
  1998年   17篇
  1997年   9篇
  1996年   13篇
  1995年   10篇
  1994年   12篇
  1993年   10篇
  1992年   26篇
  1991年   11篇
  1990年   14篇
  1989年   15篇
  1988年   11篇
  1987年   15篇
  1986年   11篇
  1985年   12篇
  1983年   6篇
  1982年   4篇
  1979年   4篇
  1975年   4篇
  1974年   4篇
  1973年   10篇
  1972年   7篇
  1971年   7篇
  1970年   4篇
  1969年   8篇
  1968年   7篇
  1966年   4篇
排序方式: 共有944条查询结果,搜索用时 0 毫秒
71.
This paper describes a stable isotope dilution method for quantification of 3-hydroxyglutaric acid (3-HGA) in body fluids. The method comprises a solid-phase extraction procedure, followed by gas chromatographic separation and negative chemical ionization mass spectrometric detection. This method is selective and sensitive, and enables measurement of 3-HGA concentrations in urine-, plasma-, and CSF- samples of controls. The control ranges for 3-HGA were: urine 0.88-4.5 mmol/mol creatinine (n=12); plasma 0.018-0.10 micro mol/l (n=10), CSF 0.022-0.067 micro mol/l (n=10). We applied this method to measure 3-HGA in body fluids of three patients with glutaric aciduria type I. We also quantified 3-HGA in amniotic fluid of controls (range 0.056-0.11 micro mol/l; n=12) and in two samples from fetuses affected with glutaric aciduria type I.  相似文献   
72.
73.
Somatostatin and somatostatin receptors in the immune system: a review   总被引:7,自引:0,他引:7  
Communication and reciprocal regulation between the nervous, endocrine and immune systems are essential for the stability of the organism. Among others, cytokines, hormones and neuropeptides have been identified as signalling molecules mediating the communication between the three systems. This review focuses on the role of the neuropeptide somatostatin as an intersystem signalling molecule, with emphasis on the immune system. Somatostatin down-modulates a number of immune functions, among others lymphocyte proliferation, immunoglobulin production and the release of proinflammatory cytokines such as IFN-g. Systemic or local treatment with somatostatin or somatostatin analogues has been shown to be beneficial in a number of in vivo models of autoimmune disease and chronic inflammation. In many of these models somatostatin appears to antagonise the effects of another neuropeptide, substance P. A somatostatin-substance P immunoregulatory circuit has been proposed to operate within murine Schistosoma mansoni-induced granulomas. In this review we extend the model of the somatostatin-substance P immunoregulatory circuit to include data derived from other biological systems, and those relying on human clinical situations. In addition, we present a hypothesis on the regulation of the default class of immune response within a tissue, based on the local balance of pro-and anti-inflammatory neuropeptides.  相似文献   
74.
Transgenic plants of the rootstock Rosa hybrida L. cv. Moneyway were produced via a two-step procedure. First, kanamycin-resistant roots were generated on stem slices from micropropagated shoots, which were cocultivated with Agrobacterium tumefaciens containing the neomycin phosphotransferase II (NPTII) gene for conferring kanamycin resistance, together with individual ROL genes from A. rhizogenes. Root formation was quite efficient and up to two kanamycin-resistant roots per stem slice were produced. In the second step, these roots were used to regenerate transgenic plants via somatic embryogenesis. Although regeneration lasted up to 12 months, production of several transformants was successfully accomplished. Untransformed escapes were not found, indicating that the initial selection on kanamycin resistance was reliable.The presence of a combination of ROLA, B and C genes enhanced adventitious root formation on micropropagated shoots and explants of stems and leaves. It appears that the auxin sensitivity was increased to such a degree that cells were able to respond even to endogenous auxins present in shoots and leaves. Rooting experiments in greenhouse demonstrated that adventitious root formation on cuttings was improved threefold upon introduction of these ROL genes. It is concluded that a method was developed for the production of ROL gene transformed roses with improved rooting characteristics.  相似文献   
75.

Background

It is suggested that the body posture during urination can influence urodynamic parameters in patients with Lower Urinary Tract Symptoms (LUTS) to an extent approaching pharmacological interventions. In this article, the influence of body position during micturition on maximum urinary flow rate (Qmax), voiding time (TQ) and post-void residual volume (PVR) in healthy males and patients with LUTS is analyzed by means of a systematic review and meta-analysis.

Evidence Acquisition

A systematic search was conducted in 14 medical databases. Studies comparing urodynamic parameters in standing versus sitting position were eligible for inclusion. Studies were stratified according to health status of included male participants: healthy individuals and patients with LUTS. Standardized mean differences for Qmax, TQ and PVR were pooled in a random effects model.

Results

Eleven articles were included. In men with LUTS, a significantly lower PVR (−24.96 ml; 95%CI −48.70 to −1.23) was shown in sitting position compared to standing. In accordance, Qmax was increased (1.23 ml/s; 95%CI −1.02 to 3.48), and TQ was decreased (−0.62 s; 95%CI −1.66 to 0.42) in sitting position, although these differences did not reach statistical significance. In healthy men, Qmax (0.18 ml/s; 95% CI −1.67 to 2.02), TQ (0.49 s; 95%CI −3.30 to 4.27) and PVR (0.43 ml; 95%CI −0.79 to 1,65) were similar in sitting and standing position.

Conclusion

For healthy men, no difference is found in any of the urodynamic parameters. In patients with LUTS, the sitting position is linked with an improved urodynamic profile.  相似文献   
76.
Up-to-date information on the prevalence and trends of common mental disorders is relevant to health care policy and planning, owing to the high burden associated with these disorders. In the first wave of the third Netherlands Mental Health Survey and Incidence Study (NEMESIS-3), a nationally representative sample was interviewed face-to-face from November 2019 to March 2022 (6,194 subjects; 1,576 interviewed before and 4,618 during the COVID-19 pandemic; age range: 18-75 years). A slightly modified version of the Composite International Diagnostic Interview 3.0 was used to assess DSM-IV and DSM-5 diagnoses. Trends in 12-month prevalence rates of DSM-IV mental disorders were examined by comparing these rates between NEMESIS-3 and NEMESIS-2 (6,646 subjects; age range: 18-64 years; interviewed from November 2007 to July 2009). Lifetime DSM-5 prevalence estimates in NEMESIS-3 were 28.6% for anxiety disorders, 27.6% for mood disorders, 16.7% for substance use disorders, and 3.6% for attention-deficit/hyperactivity disorder. Over the last 12 months, prevalence rates were 15.2%, 9.8%, 7.1%, and 3.2%, respectively. No differences in 12-month prevalence rates before vs. during the COVID-19 pandemic were found (26.7% pre-pandemic vs. 25.7% during the pandemic), even after controlling for differences in socio-demographic characteristics of the respondents interviewed in these two periods. This was the case for all four disorder categories. From 2007-2009 to 2019-2022, the 12-month prevalence rate of any DSM-IV disorder significantly increased from 17.4% to 26.1%. A stronger increase in prevalence was found for students, younger adults (18-34 years) and city dwellers. These data suggest that the prevalence of mental disorders has increased in the past decade, but this is not explained by the COVID-19 pandemic. The already high mental disorder risk of young adults has particularly further increased in recent years.  相似文献   
77.
Lactococcus lactis F10, isolated from freshwater catfish, produces a bacteriocin (BacF) active against Staphylococcus aureus, Staphylococcus carnosus, Lactobacillus curvatus, Lactobacillus plantarum, and Lactobacillus reuteri. The operon encoding BacF is located on a plasmid. Sequencing of the structural gene revealed no homology to other nisin genes. Nisin F is described.  相似文献   
78.
79.
We have addressed the mechanism of insertion of both transmembrane segments (TMs) of leader peptidase, a double-spanning protein, into the Escherichia coli inner membrane. Using photo-crosslinking, the first TM (H1) was shown to insert at a Sec-translocon/YidC interface in a fixed orientation. H1 lost its contacts with the Sec-translocon and gained access to lipids near YidC soon after complete exposure outside the ribosome. Following lipid integration, it moved away from the Sec/YidC insertion site. The second TM (H2) inserted and interacted with SecY and YidC in a similar transient fashion. The data are consistent with a linear integration model in which the TMs of polytopic inner membrane proteins move one by one from a Sec/YidC insertion site into the lipid bilayer. We propose that YidC assists the lipid partitioning of single TMs.  相似文献   
80.
A simple non-invasive method for the characterization of growth of a plant cell suspension in a single culture flask is given. The dissimilation of sugars by a cell-culture causes a loss of weight of the contents of the culture flask, and can therefore be used to follow the growth in that single culture flask. Because a correction for water evaporation is necessary, accurate results can only be obtained when a stable closure is used (e.g. Silicosen T-type plugs). The dissimilation curves obtained in this way were correlated to the concentration of sugars in the medium, the dry weight and the fresh weight. From these correlations the amount of intracellularly stored carbohydrates could be estimated. Rate constants for CO2-diffusion were determined for different types of closure. These values allowed the estimation of CO2 levels inside the culture flasks from the dissimilation curves (CO2 release curves). The dissimilation curves obtained using this method can easily be related to other types of growth curves. Different growth-phases can be clearly distinguished, e.g. lag-phase, exponential growth-phase and stationary-phase.  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