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   9882篇
  免费   616篇
  国内免费   72篇
耳鼻咽喉   107篇
儿科学   284篇
妇产科学   286篇
基础医学   1288篇
口腔科学   138篇
临床医学   811篇
内科学   2623篇
皮肤病学   267篇
神经病学   1105篇
特种医学   352篇
外科学   982篇
综合类   19篇
预防医学   605篇
眼科学   91篇
药学   645篇
中国医学   19篇
肿瘤学   948篇
  2024年   18篇
  2023年   133篇
  2022年   275篇
  2021年   416篇
  2020年   271篇
  2019年   359篇
  2018年   372篇
  2017年   288篇
  2016年   348篇
  2015年   391篇
  2014年   469篇
  2013年   578篇
  2012年   878篇
  2011年   850篇
  2010年   466篇
  2009年   395篇
  2008年   551篇
  2007年   501篇
  2006年   467篇
  2005年   408篇
  2004年   350篇
  2003年   323篇
  2002年   230篇
  2001年   84篇
  2000年   100篇
  1999年   110篇
  1998年   55篇
  1997年   34篇
  1996年   31篇
  1995年   27篇
  1994年   24篇
  1993年   32篇
  1992年   85篇
  1991年   75篇
  1990年   50篇
  1989年   72篇
  1988年   52篇
  1987年   55篇
  1986年   50篇
  1985年   57篇
  1984年   35篇
  1983年   41篇
  1981年   11篇
  1979年   16篇
  1978年   12篇
  1977年   12篇
  1973年   10篇
  1971年   13篇
  1970年   16篇
  1969年   13篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
We have analysed the collagens present in vascular basement membranes isolated from bovine retinal and cerebral microvessels and bovine renal glomeruli, and from the non-vascular basement membrane of bovine lens capsule. These are compared with the collagens produced by cultured bovine retinal microvascular pericytes and lens epithelial cells, and by canine retinal microvascular endothelial cells, in vitro. Biochemical and immunocytochemical analyses indicate that all of the vascular basement membrane preparations have an identical collagenous composition, consisting of the same polypeptides present in lens capsule (primarily type IV collagen), together with other polypeptides that are identified as type I, and a small amount of type III collagen. Identification of the latter is based on two-dimensional gel electrophoresis in the presence and absence of a reducing agent. Immunocytochemical studies, however, demonstrate type I, type IV and some type V collagen in the basement membranes of the isolated microvessels. The cultured microvascular cells produce predominantly type I collagen molecules, but they also produce other collagen peptides that appear to be type IV, and, at least in some experiments, small amounts of type III collagen. The biochemical identification of collagens type I and IV is confirmed by immunocytochemistry. However, results with anti-type I collagen and procollagen antibodies in cultured pericytes vary with antibodies from different sources. The quantities of the type IV peptides produced by the cultured cells also vary in different experiments.  相似文献   
72.
In the last 20 years, gut microbiota in patients with cystic fibrosis (CF) has become an object of interest. It was shown that these patients had gut dysbiosis and this could explain not only the intestinal manifestations of the disease but also part of those involving the respiratory tract. The acquisition of previously unknown information about the importance of some bacteria, i.e., those partially or totally disappeared in the gut of CF patients, in the regulation of the activity and function of the gut and the lung was the base to suggest the use of probiotics in CF patients. The main aim of this paper is to discuss the biological basis for probiotic administration to CF patients and which results could be expected. Literature analysis showed that CF intestinal dysbiosis depends on the same genetic mutations that condition the clinical picture of the diseases and is aggravated by a series of therapeutic interventions, such as dietary modifications, the use of antibiotics, and the administration of antacids. All this translates into a significant worsening of the structure and function of organs, including the lung and intestine, already deeply penalized by the genetic alterations of CF. Probiotics can intervene on dysbiosis, reducing the negative effects derived from it. However, the available data cannot be considered sufficient to indicate that these bacteria are essential elements of CF therapy. Further studies that take into account the still unsolved aspects on how to use probiotics are absolutely necessary.  相似文献   
73.
Type 4 phosphodiesterases (PDE4) inhibitors are emerging therapeutics in the treatment of a number of chronic disorders including asthma, chronic obstructive pulmonary disease (COPD) and cognitive disorders. This study delineates the preclinical profile of L-454,560, which is a potent, competitive and preferential inhibitor of PDE4A, 4B, and 4D with IC50 values of 1.6, 0.5 and 1.2 nM, respectively. In contrast to the exclusive binding of cilomilast and the preferential binding of roflumilast to the PDE4 holoenzyme state (Mg2+-bound form), L-454,560 binds to both the apo-(Mg2+-free) and holoenzyme states of PDE4. The intrinsic enzyme potency for PDE4 inhibition by L-454,560 also results in an effective blockade of LPS-induced TNFalpha formation in whole blood (IC50 = 161 nM) and is comparable to the human whole blood potency of roflumilast. The cytokine profile of inhibition of L-454,560 is mainly a Th1 profile with significant inhibition of IFNgamma and no detectable inhibition of IL-13 formation up to 1 microM. L-454,560 was also found to be efficacious in two models of airway hyper-reactivity, the ovalbumin (OVA) sensitized and challenged guinea pig and the ascaris sensitized sheep model. Furthermore, L-454560 was also effective in improving performance in the delayed matching to position (DMTP) version of the Morris watermaze, at a dose removed from that associated with potential emesis. Therefore, L-454,560 is a novel PDE4 inhibitor with an overall in vivo efficacy profile at least comparable to roflumilast and clearly superior to cilomilast.  相似文献   
74.
75.

Objective

The objective of this multicentre, non-controlled, open-label study is the evaluation of the bleeding patterns during the use of a vaginal combined contraceptive, its safety in relation to occurrence of adverse effects, its efficacy as a contraceptive method and user compliance.

Study design

Healthy female volunteers (N = 165), asking for contraception, were enrolled to participate in the study. Each subject was given seven vaginal rings, releasing an average amount of 120 μg etonogestrel (ENG) and 15 μg ethinylestradiol (EE) per day. Study period was 7 cycles. A total of 878 cycles was valid for statistical analysis. The primary parameter, (breakthrough bleeding and/or spotting), was recorded for each cycle. The subjects were asked to report any adverse effect experienced during the treatment period, general physical and gynaecological examinations were performed and haematological blood tests were taken.

Results

Breakthrough bleeding/spotting occurred in 5.01% cycles (44 out of 878 cycles, of whom 37 were breakthrough spotting only). Absence of withdrawal bleeding during the ring-free period was reported in 1.94% cycles (17 out of 878). Forty-one subjects (24.8%) reported 66 events that were potentially drug-related. The most frequently drug-related events were weight increase (10 cases), headache (9 cases), nausea (4 cases). No pregnancy was reported during the study period. Haematology and chemical chemistry tests showed no clinically significant abnormality.

Conclusions

In the present study, NuvaRing® has shown to be a valid contraceptive method to ensure optimal cycle control with low incidence of irregular bleeding and altered withdrawal bleeding. The low incidence of gastrointestinal side effects (nausea, vomiting) may be related the low hormonal dose and to the vaginal delivery of hormones which avoids the gastrointestinal tract.  相似文献   
76.
Fertility preservation in young girls affected by malignancies has got growing relevance in the last decade due to the improved survival chance of these patients after oncostatic treatments. Most studies have focused on preserving ovarian follicles and avoiding premature ovarian failure, whereas only a few have evaluated the effects exerted by radiotherapy and chemotherapy on the uterus. It is self-evident that fertility preservation after oncostatic therapies must include the maintenance of a functional uterus, and a certain degree of uterine damage must be considered when estimating reproductive prognosis in previously treated, childhood cancer survivors. TARGET AUDIENCE: Obstetricians & Gynecologists, Family Physicians. LEARNING OBJECTIVES: After completion of this article, the reader should be able to recall the growing number of children who survive oncostatic treatments, explain the possible effects on future reproductive endeavors, and summarize the possible ways to preserve fertility.  相似文献   
77.
This article focuses on agar biopolymer films that offer promise for developing biodegradable packaging, an important solution for reducing plastics pollution. At present there is a lack of data on the mechanical performance of agar biopolymer films using a simple plasticizer. This study takes a Design of Experiments approach to analyze how agar-glycerin biopolymer films perform across a range of ingredients concentrations in terms of their strength, elasticity, and ductility. Our results demonstrate that by systematically varying the quantity of agar and glycerin, tensile properties can be achieved that are comparable to agar-based materials with more complex formulations. Not only does our study significantly broaden the amount of data available on the range of mechanical performance that can be achieved with simple agar biopolymer films, but the data can also be used to guide further optimization efforts that start with a basic formulation that performs well on certain property dimensions. We also find that select formulations have similar tensile properties to thermoplastic starch (TPS), acrylonitrile butadiene styrene (ABS), and polypropylene (PP), indicating potential suitability for select packaging applications. We use our experimental dataset to train a neural network regression model that predicts the Young’s modulus, ultimate tensile strength, and elongation at break of agar biopolymer films given their composition. Our findings support the development of further data-driven design and fabrication workflows.  相似文献   
78.
BackgroundPeptide receptor radionuclide therapy (PRRT) with radiolabeled somatostatin receptor (SSR) analogs is now an established systemic treatment for neuroendocrine tumors (NET). However, more short- and long-term data about renal and hepatotoxicity is needed. Here we present our experience in this clinical scenario.MethodsEighty-six patients with progressive SSR-expressing malignancies underwent PRRT with Lu-177 Dotatate and were followed up for up to 2 years. Laboratory tests were done 1 week before each cycle and every 2 months at follow-up. Hepatic and renal toxicity was determined based on NCI CTCAE V5.0.Results55/86 (64%) patients completed all 4 cycles of PRRT; 18/86 (20.9%) are currently being treated; 13/86 (15.1%) had to discontinue PRRT: 4/13 (31%) due to hematologic toxicity, 9/13 (69%) due to non-PRRT-related comorbidities. Out of the patients who finished treatment, only transient grade 2 toxicities were observed during PRRT: hypoalbuminemia in 5.5% (3/55), and renal toxicity (serum creatinine and estimated glomerular filtration rate) in 1.8% (1/55). No grade 3 or 4 liver and renal toxicity occurred. Patients presenting with impaired liver or renal function prior to PRRT, either improved or had stable findings. No deterioration was observed.ConclusionPeptide receptor radionuclide therapy does not have a negative impact on liver and renal function, even in patients with pre-existing impaired parameters. No grade 3 or 4 hepatic or renal toxicity was identified. Only transient grade 2 hypoalbuminemia in 5.5% and nephrotoxicity in 1.8% of patients were seen during PRRT.  相似文献   
79.
We have previously reported the anticarcinogenic effects of an olive fruit extract composed of pentacyclic triterpenes, the main components of which are maslinic acid (73.25%) and oleanolic acid (25.75%). Here we examined the effects of the individual components on proliferation, necrosis and apoptosis rates by fluorescence-based techniques in human HT-29 colon cancer cells. Oleanolic acid showed moderate antiproliferative activity, with an ec50 of 160.6 (se 10.6) micromol/l, and moderate cytotoxicity at high concentrations ( > or = 250 micromol/l). On the other hand, maslinic acid inhibited cell growth with an ec50 of 101.2 (se 7.8) micromol/l, without necrotic effects. Oleanolic acid, which lacks a hydroxyl group at the carbon 2 position, failed to activate caspase-3 as a prime apoptosis protease. In contrast, maslinic acid increased caspase-3-like activity at 10, 25 and 50 micromol/l by 3-, 3.5- and 5-fold over control cells, respectively. The detection of ROS in the mitochondria, which serve as pro-apoptotic signal, evidenced the different bioactivity of the two triterpenes. Confocal microscopy analysis revealed that maslinic acid generated superoxide anions while oleanolic acid-treated cells did not differ from the control. Completion of apoptosis by maslinic acid was confirmed microscopically by the increase in plasma membrane permeability, and detection of DNA fragmentation. In conclusion, the anticancer activity observed for olive fruit extracts seems to originate from maslinic acid but not from oleanolic acid. Maslinic acid therefore is a promising new compound for the chemoprevention of colon cancers.  相似文献   
80.
Treatment of herpes simplex virus type 1 (HSV-1) infected Vero, BHK, BHKtk- and LMtk- cells with 5-iodo-5'-amino-2',5'-dideoxyuridine (AIdUrd) caused increased synthesis of ICP36 and an increase in HSV-1 thymidine kinase (tk) activity at late times of infection. The overproduced ICP36 was identified as the HSV-1 encoded tk protein by immunoprecipitation. Whereas the thymidine analogue 5'-amino-5'-deoxythymidine (AdThd) caused an increase in HSV-1 tk synthesis and activity in wild type Vero and BHK cells, 5-iodo-2'-deoxyuridine (IdUrd) caused a similar increase only in tk- cells (LMtk-, BHKtk-). In vivo and in vitro stabilization studies using a [35S]methionine pulse-chase experiment or heat inactivation studies with purified HSV-1 tk revealed that stabilization of tk by the analogues could not account for the extent of the observed increase. Since overproduction of tk is observed only at late times of infection, it is suggested that the presence of these thymidine analogues in either the viral DNA or the cellular nucleotide pools is responsible for the observed differential effects.  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