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   2383篇
  免费   192篇
  国内免费   1篇
  2023年   7篇
  2022年   4篇
  2021年   45篇
  2020年   21篇
  2019年   21篇
  2018年   41篇
  2017年   29篇
  2016年   75篇
  2015年   125篇
  2014年   130篇
  2013年   169篇
  2012年   224篇
  2011年   219篇
  2010年   138篇
  2009年   121篇
  2008年   153篇
  2007年   163篇
  2006年   126篇
  2005年   130篇
  2004年   122篇
  2003年   107篇
  2002年   102篇
  2001年   22篇
  2000年   14篇
  1999年   13篇
  1998年   27篇
  1997年   22篇
  1996年   15篇
  1995年   19篇
  1994年   14篇
  1993年   12篇
  1992年   12篇
  1991年   11篇
  1990年   6篇
  1989年   7篇
  1987年   6篇
  1986年   4篇
  1985年   8篇
  1984年   5篇
  1983年   9篇
  1982年   10篇
  1981年   3篇
  1980年   8篇
  1979年   4篇
  1978年   6篇
  1977年   5篇
  1976年   9篇
  1975年   6篇
  1974年   4篇
  1971年   4篇
排序方式: 共有2576条查询结果,搜索用时 140 毫秒
61.
Summary

The hyphomycete spora of the River Kelvin and its tributary, the Allander Water, was sampled during October 1986 to January 1987. Twenty spore types were found, the commonest being Flagellospora curvula and Lemonniera aquatica. Spore numbers were high in October and declined during the autumn to an undetectable level by the end of December, but leaves collected in December and January yielded spores on incubation in water.  相似文献   
62.

Background

Access to Cognitive behavioural therapy (CBT) for depression is limited. One solution is CBT self-help books. Trial Objectives: To assess the impact of a guided self-help CBT book (GSH-CBT) on mood, compared to treatment as usual (TAU).Hypotheses:
  1. GSH-CBT will have improved mood and knowledge of the causes and treatment of depression compared to the control receiving TAU
  2. Guided self-help will be acceptable to patients and staff.

Methods and Findings

Participants: Adults attending seven general practices in Glasgow, UK with a BDI-II score of ≥14. 141 randomised to GSH-CBT and 140 to TAU. Interventions: RCT comparing ‘Overcoming Depression: A Five Areas Approach’ book plus 3–4 short face to face support appointments totalling up to 2 hours of guided support, compared with general practitioner TAU. Primary outcome: The BDI (II) score at 4 months. Numbers analysed: 281 at baseline, 203 at 4 months (primary outcome), 117 at 12 months. Outcome: Mean BDI-II scores were lower in the GSH-CBT group at 4 months by 5.3 points (2.6 to 7.9, p<0.001). At 4 and 12 months there were also significantly higher proportions of participants achieving a 50% reduction in BDI-II in the GSH-CBT arm. The mean support was 2 sessions with 42.7 minutes for session 1, 41.4 minutes for session 2 and 40.2 minutes of support for session 3. Adverse effects/Harms: Significantly less deterioration in mood in GSH-CBT (2.0% compared to 9.8% in the TAU group for BDI—II category change).

Limitations

Weaknesses: Our follow-up rate of 72.2% at 4 months is better than predicted but is poorer at 12 months (41.6%). In the GSH-CBT arm, around 50% of people attended 2 or fewer sessions. 22% failed to take up treatment.

Conclusions

GSH-CBT is substantially more effective than TAU.

Trial Registration

Controlled-Trials.com ISRCTN13475030  相似文献   
63.
Whereas fossil evidence indicates extensive treeless vegetation and diverse grazing megafauna in Europe and northern Asia during the last glacial, experiments combining vegetation models and climate models have to-date simulated widespread persistence of trees. Resolving this conflict is key to understanding both last glacial ecosystems and extinction of most of the mega-herbivores. Using a dynamic vegetation model (DVM) we explored the implications of the differing climatic conditions generated by a general circulation model (GCM) in “normal” and “hosing” experiments. Whilst the former approximate interstadial conditions, the latter, designed to mimic Heinrich Events, approximate stadial conditions. The “hosing” experiments gave simulated European vegetation much closer in composition to that inferred from fossil evidence than did the “normal” experiments. Given the short duration of interstadials, and the rate at which forest cover expanded during the late-glacial and early Holocene, our results demonstrate the importance of millennial variability in determining the character of last glacial ecosystems.  相似文献   
64.

Background

Surgical site infections (SSI’s) are associated with severe morbidity, mortality and increased health care costs in vascular surgery.

Objective

To implement a bundle of care in vascular surgery and measure the effects on the overall and deep-SSI’s rates.

Design

Prospective, quasi-experimental, cohort study.

Methods

A prospective surveillance for SSI’s after vascular surgery was performed in the Amphia hospital in Breda, from 2009 through 2011. A bundle developed by the Dutch hospital patient safety program (DHPSP) was introduced in 2009. The elements of the bundle were (1) perioperative normothermia, (2) hair removal before surgery, (3) the use of perioperative antibiotic prophylaxis and (4) discipline in the operating room. Bundle compliance was measured every 3 months in a random sample of surgical procedures and this was used for feedback.

Results

Bundle compliance improved significantly from an average of 10% in 2009 to 60% in 2011. In total, 720 vascular procedures were performed during the study period and 75 (10.4%) SSI were observed. Deep SSI occurred in 25 (3.5%) patients. Patients with SSI’s (28,5±29.3 vs 10.8±11.3, p<0.001) and deep-SSI’s (48.3±39.4 vs 11.4±11.8, p<0.001) had a significantly longer length of hospital stay after surgery than patients without an infection. A significantly higher mortality was observed in patients who developed a deep SSI (Adjusted OR: 2.96, 95% confidence interval 1.32–6.63). Multivariate analysis showed a significant and independent decrease of the SSI-rate over time that paralleled the introduction of the bundle. The SSI-rate was 51% lower in 2011 compared to 2009.

Conclusion

The implementation of the bundle was associated with improved compliance over time and a 51% reduction of the SSI-rate in vascular procedures. The bundle did not require expensive or potentially harmful interventions and is therefore an important tool to improve patient safety and reduce SSI’s in patients undergoing vascular surgery.  相似文献   
65.
Respiratory motion during percutaneous radiotherapy can be considered based on respiration-correlated computed tomography (4DCT). However, most treatment planning systems perform the dose calculation based on a single primary CT data set, even though cine mode displays may allow for a visualisation of the complete breathing cycle. This might create the mistaken impression that the dose distribution were independent of tumour motion. We present a movie visualisation technique with the aim to direct attention to the fact that the dose distribution migrates to some degree with the tumour and discuss consequences for gated treatment, IMRT plans and flattening-filter-free beams. This is a feasibility test for a visualisation of tumour and isodose motion. Ten respiratory phases are distinguished on the CT, and the dose distribution from a stationary IMRT plan is calculated on each phase, to be integrated into a movie of tumour and dose motion during breathing. For one example patient out of the sample of five lesions, the plan is compared with a gated treatment plan with respect to tumour coverage and lung sparing. The interplay-effect for small segments in the IMRT plan is estimated. While the high dose rate, together with the cone-shaped beam profile, makes the use of flattening-filter-free beams more problematic for conformal and IMRT treatment, it can be the option of choice if gated treatment is preferred. The different effects of respiratory motion, dose build-up and beam properties (segments and flatness) for gated vs. un-gated treatment can best be considered if planning is performed on the full 4DCT data set, which may be an incentive for future developments of treatment planning systems.  相似文献   
66.
67.
With the aim to adapt high‐yield adherent cell lines to suspension growth, Madin Darby canine kidney (MDCK) suspension cells were developed recently that achieved comparable influenza virus yields despite an early induction of apoptosis compared to the parental adherent cell line. For both cell lines, a comprehensive study under comparable infection conditions is performed comprising information on: time course of viral infection, antiviral state of cells, virus‐induced apoptosis, and virus‐induced cellular protein expression for early and late infection with influenza A/PuertoRico/8/34 H1N1. The proteomic analysis is performed with 2D differential gel electrophoreses followed by mass spectrometry. Based on flow cytometric data and on the differential expression of various stress and apoptosis‐related proteins, the earlier onset of virus‐induced apoptosis is confirmed for suspension cells. Surprisingly, the data indicated an increased virus release rate for suspension cells. These observations correlate with an increased expression of the apical marker protein ezrin, known to play a role in influenza‐induced cytoskeletal rearrangement, and the differential expression of heterogeneous nuclear ribonucleoproteins, known to bind actively influenza viral proteins and play a central role in regulating gene expression. Based on these findings, additional studies towards the design of MDCK suspension cells with further increase in influenza virus yields will be performed.  相似文献   
68.
69.
We describe a simple protocol for identifying and quantifying the two components in binary mixtures of species possessing one or more similar proteins. Central to the method is the identification of ''corresponding proteins'' in the species of interest, in other words proteins that are nominally the same but possess species-specific sequence differences. When subject to proteolysis, corresponding proteins will give rise to some peptides which are likewise similar but with species-specific variants. These are ''corresponding peptides''. Species-specific peptides can be used as markers for species determination, while pairs of corresponding peptides permit relative quantitation of two species in a mixture. The peptides are detected using multiple reaction monitoring (MRM) mass spectrometry, a highly specific technique that enables peptide-based species determination even in complex systems. In addition, the ratio of MRM peak areas deriving from corresponding peptides supports relative quantitation. Since corresponding proteins and peptides will, in the main, behave similarly in both processing and in experimental extraction and sample preparation, the relative quantitation should remain comparatively robust. In addition, this approach does not need the standards and calibrations required by absolute quantitation methods. The protocol is described in the context of red meats, which have convenient corresponding proteins in the form of their respective myoglobins. This application is relevant to food fraud detection: the method can detect 1% weight for weight of horse meat in beef. The corresponding protein, corresponding peptide (CPCP) relative quantitation using MRM peak area ratios gives good estimates of the weight for weight composition of a horse plus beef mixture.  相似文献   
70.
Human pluripotent stem cells (hPSCs) represent a platform to study human development in vitro under both normal and disease conditions. Researchers can direct the differentiation of hPSCs into the cell type of interest by manipulating the culture conditions to recapitulate signals seen during development. One such cell type is the melanocyte, a pigment-producing cell of neural crest (NC) origin responsible for protecting the skin against UV irradiation. This protocol presents an extension of a currently available in vitro Neural Crest differentiation protocol from hPSCs to further differentiate NC into fully pigmented melanocytes. Melanocyte precursors can be enriched from the Neural Crest protocol via a timed exposure to activators of WNT, BMP, and EDN3 signaling under dual-SMAD-inhibition conditions. The resultant melanocyte precursors are then purified and matured into fully pigmented melanocytes by culture in a selective medium. The resultant melanocytes are fully pigmented and stain appropriately for proteins characteristic of mature melanocytes.  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