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   1493篇
  免费   139篇
  1632篇
  2022年   9篇
  2021年   18篇
  2020年   11篇
  2019年   16篇
  2018年   26篇
  2017年   25篇
  2016年   34篇
  2015年   61篇
  2014年   58篇
  2013年   112篇
  2012年   92篇
  2011年   90篇
  2010年   68篇
  2009年   51篇
  2008年   64篇
  2007年   66篇
  2006年   53篇
  2005年   77篇
  2004年   61篇
  2003年   52篇
  2002年   48篇
  2001年   37篇
  2000年   40篇
  1999年   35篇
  1998年   21篇
  1997年   29篇
  1996年   30篇
  1995年   20篇
  1994年   16篇
  1993年   20篇
  1992年   34篇
  1991年   30篇
  1990年   23篇
  1989年   20篇
  1988年   14篇
  1987年   14篇
  1986年   23篇
  1985年   13篇
  1984年   10篇
  1983年   8篇
  1982年   8篇
  1980年   5篇
  1979年   11篇
  1977年   10篇
  1976年   7篇
  1975年   9篇
  1974年   5篇
  1969年   6篇
  1968年   8篇
  1965年   4篇
排序方式: 共有1632条查询结果,搜索用时 0 毫秒
51.
There is recent evidence that mouse and human spermatozoa contain constitutive nitric oxide synthase (cNOS) and can synthesize nitric oxide. The aim of this study was to investigate whether the inhibition of human sperm cNOS could affect sperm-oocyte fusion and sperm binding to the zona pellucida (ZP). N(G)-nitro-L-arginine methyl ester (L-NAME) was used as cNOS inhibitor. Sperm-oocyte fusion was evaluated using the hamster egg penetration test (HEPT). The ZP binding was evaluated using the hemizona assay. L-NAME added from the onset of capacitation strongly inhibited sperm-oocyte fusion. This inhibitory effect was dose dependent, stereospecific, and suppressed by L-arginine in a dose-dependent manner. L-NAME also inhibited sperm-oocyte fusion in the HEPT enhanced with progesterone (P), where P (5 microM) was added for 15 min to capacitated sperm. A lesser but significant inhibition was also observed when sperm suspensions were exposed to L-NAME following capacitation in both versions of HEPT. On the contrary, L-NAME did not affect ZP binding. In conclusion, the present study provides the evidence that cNOS plays a role in the human sperm's capacity to fuse with oocyte but not in the ZP binding.  相似文献   
52.
53.
54.
The Le Fort fracture without maxillary mobility constitutes 9 percent of maxillary fractures observed over a 3-year period. A high Le Fort (level II or III) injury exists as a one- or two-piece incomplete fracture. The degree of fracture is insufficient to permit mobility of the maxillary alveolus. Frequently, an obvious unilateral zygomatic fracture is present. Physical findings consist of bilateral eyelid ecchymosis and malocclusion. The occlusal disturbance may consist of either crossbite, open bite, maxillary rotation, or lack of proper dental intercuspation. On CT scan, fractures are best demonstrated in the posterior and medial maxillary walls at the Le Fort I level; they are most obvious unilaterally with contralateral fractures that may be subtle. Bilateral maxillary sinus fluid is consistently present on CT. Treatment usually consists of observation and traction elastics but may require mobilization of the fragments followed by open reduction and rigid fixation.  相似文献   
55.
Continuous pollen monitoring of an urban network consisting of three stations has been undertaken for a period of 2 years in Perugia, central Italy. The aim has been to establish whether the Perugia pollen trap, active since 1983, is still representative of the area following recent urbanisation. Quantitative differences were found between the stations, reflecting different vegetational areas, but only slight differences were detected in relation to the timing of the principal period of pollination. Therefore, although individual pollen traps are necessary to characterize fully the different areas, one trap is sufficient to determine the key allergenic thresholds in the studied area.  相似文献   
56.
There is evidence that severe dengue disease is associated with alterations of the microvascular endothelium. We examined the hypothesis that activation and damage of microvascular endothelial cells (EC) could be induced by inflammatory mediators present in dengue patient's sera. We cultured human microvascular EC (HMEC-1) in vitro with sera from patients with acute dengue infection. Sera from patients with acute dengue induced an increase in ICAM-1 expression on HMEC-1. This effect was greater with samples from the acute febrile phase than with samples from the convalescent phase of the disease. Acute dengue sera had elevated levels of TNF-alpha and the endothelial activating effect of acute dengue sera was inhibited up to 80% by pre-treatment with monoclonal antibodies against TNF-alpha. Furthermore, acute dengue sera induced apoptosis in HMEC-1. These findings support the pathophysiologic significance of microvascular EC and serum inflammatory mediators in dengue.  相似文献   
57.
In this study we examined hormonal responses of Black-legged Kittiwake (Rissatridactyla) chicks to experimental variations in energy content and nutritional quality (low or high lipid to protein ratio, LPR) of their food. Starting at the age of 10 days, chicks were fed either high or low LPR fish at 30, 50, 70 and 100% of ad libitum energy intake. After 20 days of treatment, chicks were exposed to a standardized acute handling and restraint stress protocol, where a baseline sample was taken immediately after taking a chick from the nest, and three additional blood samples were taken at intervals up to 50 min. Testosterone and corticosterone titres in plasma were measured via radioimmunoassay. We found that baseline testosterone levels were not significantly affected by the experimental treatments. Food-restricted chicks had elevated baseline and acute stress-induced levels of corticosterone compared to chicks fed ad libitum. An elevation of circulating levels of corticosterone in energetically stressed individuals was further magnified by low nutritional quality of food. Baseline and acute stress-induced corticosterone levels of chicks were negatively correlated with their fat reserves. We conclude that the physiological condition of Black-legged Kittiwake chicks can be assessed reliably by measuring circulating levels of corticosterone. We discuss short- and long-term effects of elevated corticosterone secretion in food-stressed nest-bound chicks. Accepted: 13 April 1999  相似文献   
58.
In Western countries, therapeutic management of patients affected by choroidal neovascularization (CNV) secondary to different typologies of macular degeneration represents a major health care problem. Age-related macular degeneration is the disease most frequently associated with CNV development. Schematically, CNVs can be distinguished into classic and occult subtypes, which are characterized by variable natural history and different responsiveness to some therapeutic procedures. At present, the dramatic vision loss due to CNV can be mainly treated by two interventional strategies, which are utilizable in either single or combined modalities: photodynamic therapy with verteporfin (PDT-V), and intravitreal administration of drugs acting against vascular endothelial growth factor. The combined use of PDT-V and anti-angiogenic drugs represents one of the most promising strategies against neovascular macular degeneration, but it unavoidably results in an expensive increase in health resource utilization. However, the positive data from several studies serve as a basis for reconsidering the role of PDT-V, which has undergone a renaissance prompted by the need for a more rational therapeutic approach toward CNV. New pharmacogenetic knowledge of PDT-V points to exploratory prospects to optimize the clinical application of this intriguing photothrombotic procedure. In fact, a Medline search provides data regarding the role of several single nucleotide polymorphisms (SNPs) as genetic predictors of CNV responsiveness to PDT-V. Specifically, correlations between SNPs and different levels of PDT-V efficacy have been detected by examining the gene variants influencing (i) thrombo-coagulative pathways, i.e. methylenetetrahydrofolate reductase (MTHFR) 677C>T (rs1801133), factor V (F5) 1691G>A (rs6025), prothrombin (F2) 20210G>A (rs1799963), and factor XIII-A (F13A1) 185G>T (rs5985); (ii) complement activation and/or inflammatory processes, i.e. complement factor H (CFH) 1277T>C (rs1061170), high-temperature requirement factor A1 (HTRA1) promoter -512G>A (rs11200638), and two variants of the C-reactive protein (CRP) gene (rs2808635 and rs876538); and (iii) production and bioavailability of vascular endothelial growth factor (VEGFA -2578C>A [rs699947] and rs2146323). This article critically evaluates both the clinical plausibility and the opportunity to utilize the most important SNP-response interactions of PDT-V for an effective upgrade of the current anti-CNV therapeutic scenario. In addition, the pharmacogenetics of a very severe post-PDT-V adverse event, i.e. a decrease in acute vision, is briefly discussed. A comprehensive appraisal of the findings reviewed in this article should be carefully considered to design future trials aimed at verifying (after proper genotypic stratification of the enrolled patients) whether these innovative pharmacogenetic approaches will be able to improve the multifaceted interventional management of neovascular macular degeneration.  相似文献   
59.
In the lizard Podarcis sicula, the major vitellogenin (VTG)-derived yolk proteins, lipovitellins and phosvitins, were extracted from the yolk globules of laid and fertilized eggs at different periods of incubation up to 44 days close to hatching. Embryonic development was almost over at this time. Yolk proteins were isolated by precipitation in saturated (NH(4))(2)SO(4), separated on SDS-PAGE and detected by Western blotting with homologous polyclonal anti/VTG antibody. Two lipovitellins of 110 and 116 kDa were always present in the yolk of laid eggs after 1, 10, 18, and 44 days from oviposition. Both these proteins were glycosylated and were recognized by the anti/VTG antibody; their N-terminal sequences were analyzed. Four phosvitins were detected in freshly laid eggs, but their number decreased during incubation, and after 44 days only a single protein of approximately 6.5 kDa was present. The results indicated that, in this lizard, during embryonic development, lipovitellins remain unchanged, whereas the phosphorylated components of yolk undergo continuous degradation.  相似文献   
60.
A morphological and morphometrical study has been carried out on glomerular lesions in mink with spontaneous Aleutian disease, using the WHO classification for Systemic Lupus Erytematous Nefritis. 154 renal samples from sick animals and 10 samples from uninfected mink were processed by routine histopathological techniques and metacrylate inclusions. The samples were studied quantitatively with an automatic image analyzer. 5 forms of glomerulonephritis (GN) were identified: mesangial glomerulonephritis (n = 13), focal and segmental GN (n = 10), diffuse GN (n = 99), membranous GN (n = 12) and advanced sclerosing GN (n = 10) and were associated with the degree of interstitial plasmocytosis. Glomerule morphometry was shown to be an excellent method for identifying the type of lesion, while it quantified the participation of various glomerular elements in the lesion.  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