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   1352篇
  免费   83篇
  2023年   7篇
  2022年   16篇
  2021年   26篇
  2020年   16篇
  2019年   21篇
  2018年   28篇
  2017年   20篇
  2016年   54篇
  2015年   51篇
  2014年   64篇
  2013年   77篇
  2012年   113篇
  2011年   114篇
  2010年   74篇
  2009年   51篇
  2008年   86篇
  2007年   86篇
  2006年   86篇
  2005年   56篇
  2004年   57篇
  2003年   61篇
  2002年   53篇
  2001年   18篇
  2000年   8篇
  1999年   19篇
  1998年   12篇
  1997年   14篇
  1996年   14篇
  1995年   8篇
  1994年   11篇
  1993年   7篇
  1992年   9篇
  1991年   8篇
  1990年   7篇
  1989年   6篇
  1988年   10篇
  1987年   12篇
  1986年   8篇
  1985年   6篇
  1984年   3篇
  1983年   4篇
  1981年   3篇
  1979年   3篇
  1976年   3篇
  1975年   2篇
  1974年   2篇
  1973年   2篇
  1971年   4篇
  1970年   3篇
  1969年   5篇
排序方式: 共有1435条查询结果,搜索用时 15 毫秒
1.
In a multicentre, randomised, prospective trial 89 patients (67 children and 22 adults) with the minimal change nephrotic syndrome were treated with three intravenous pulses of methylprednisolone followed by low dose oral prednisone for six months (group given methylprednisolone) or with high dose oral prednisone for four weeks followed by low dose oral prednisone for five months (control group). Five patients in the group given methylprednisolone and one in the control group did not respond initially. The time to response was shorter in children treated with methylprednisolone. No significant differences between the two groups were observed in the number of patients who relapsed or number of relapses per patient per year. Patients given methylprednisolone tended to relapse earlier than patients in the control group. Side effects related to treatment were significantly fewer in the group given methylprednisolone than in the control group. These data suggest that a short course of methylprednisolone pulses followed by low dose oral prednisone is only marginally less effective than a regimen of high dose oral steroids but can improve the ratio of risk to benefit associated with treatment of the minimal change nephrotic syndrome.  相似文献   
2.
Abstract

Brassica rupestris Raf. is a chasmophyte species that includes two subspecies, both endemic to Central-Western Sicily (Italy). Inter-Simple Sequence Repeat (ISSR) markers were used to detect genetic diversity within and among eight populations representative of the species' distribution range. High levels of genetic diversity were revealed both at the population (PPB = 53.88%, H S = 0.212, Sh = 0.309) and at the species level (PPB = 96.55%, H T = 0.307, Sh = 0.464). The correlation between genetic and geographical distances was negative (Mantel test, r = ?0.06, P < 0.95). The two subspecies of B. rupestris, subsp. rupestris and subsp. hispida, showed remarkable genetic similarity and molecular data did not unequivocally support their distinctness. The pattern of genetic variation revealed by our study bears important consequences for conservation management: It is desirable to preserve B. rupestris populations in situ with a “dynamic” strategy, while, ex situ conservation programmes might be improved to safeguard maximum genetic diversity.  相似文献   
3.
4.
The oculogyric nerves contain afferent fibers originating from the ophthalmic territory, the somata of which are located in the ipsilateral semilunar ganglion. These primary sensory neurons project to the Subnucleus Gelatinosus of the Nucleus Caudalis Trigemini, where they make presynaptic contact with the central endings of the primary trigeminal afferents running in the fifth cranial nerve. After complete section of the trigeminal root, the antidromic volleys elicited in the trunk of the third cranial nerve by stimulating SG of NCT consisted of two waves belonging to the A delta and C groups. The area of both components of the antidromic volleys decreased both after bradykinin and hystamine injection into the corresponding cutaneous region and after thermic stimulation of the ipsilateral trigeminal ophthalmic territory. The reduction of such potentials can be explained in terms of collision between the antidromic volleys and those elicited orthodromically by chemical and thermic stimulation. Also, capsaicin applied on the nerve induced an immediate increase, followed by a long lasting decrease, of orthodromic evoked response area. These findings bring further support to the nociceptive nature of the afferent fibers running into the oculomotor nerve.  相似文献   
5.
Summary Photoautotrophic picoplankton is reported from some lakes located near the Italian Antarctic station of Terra Nova. Observations, carried out by both flow cytometry on water samples and electron microscopy on micro-organisms in cultures from each lake, have confirmed the occurrence in all the environments studied of this fraction accounting, in several cases, for more than the 50% of the phytoplankton, measured as chlorophyll. Cultures of the picoplankton fraction from these waters contained known prokaryotic (Synechococcus) and eukaryotic (Chlorella) genera as well as two unidentified entities, possibly prochlorophytes.  相似文献   
6.
Commercially available and affinity-purified butyrylcholinesterases isolated from human serum were examined for their esterasic activity and their ability to hydrolyze various neuropeptides, including neurotensin, substance P, and leucine-enkephalin. The three pools that displayed the lowest esterasic activities were shown to hydrolyze neurotensin with the same HPLC degradative pattern. By contrast, noticeable qualitative and quantitative discrepancies were observed when hydrolyses of substance P and leucine-enkephalin by these three butyrylcholinesterase pools were studied. The pool that exhibited the highest esterasic activity appeared to be homogeneously constituted by 90- and 180-kDa protein bands by sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis and was totally unable to hydrolyze these three neuropeptides. This suggested that the three other butyrylcholinesterase preparations could be contaminated by exogenous peptidases. This was confirmed by means of three distinct monoclonal antibodies directed toward human serum butyrylcholinesterase. The three IgG-purified fractions precipitated the esterasic activity, whereas they failed to precipitate the neuropeptide-hydrolyzing activities whatever the substrate examined. Altogether, these results demonstrate that peptidases associated with butyrylcholinesterase are contaminating enzymes that cannot be considered as intrinsic activities of this enzyme.  相似文献   
7.
Pre-treatment of human lymphocytes with 17-estradiol diminishes the increase in concentration of cytosolic free calcium after stimulation with phytohaemagglutinin. The effect is dependent on 17-estradiol concentration and on the preincubation time. The effect is not due to an interaction between 17-estradiol and phytohaemagglutinin, but appears to be a consequence of the binding of the hormone to the cell surface. The effect is specific for 17-estradiol, since the isomer and other steroid hormones (progesterone, testosterone, diethylstilbestrol and 5-androstan), have no effect. Since the effect of the 17-estradiol can be suppressed by treatment of lymphocytes with ouabain, it appears that the effect of estradiol on the rise of cytosolic calcium induced by phytohaemagglutinin is mediated by the (Na, K)-ATPase.  相似文献   
8.
Human eccrine sweat devoid of epidermal protein contamination was collected from palms, soles, and different sites on the trunk. Interleukin 1 alpha (IL 1 alpha) and interleukin 1 beta (IL 1 beta) content were analyzed for immunoreactivity by enzymo-immunoassay and immunoblotting and for bioactivity by the stimulation of prostaglandin E2 (PGE2) production in human dermal fibroblasts. The bioassay was validated by using blocking antibodies against IL 1 alpha and beta. All sweat samples were found to contain significant amounts of immunoreactive and biologically active IL 1. The immunoreactive forms were at 17 kDa as shown by immunoblotting analysis, indicating that they were mature (secreted), undegraded IL 1 peptides. Whereas IL 1 alpha was detectable in sweat samples obtained from both truncal and palmo-plantar regions, IL 1 beta was only detectable in the sweat of palms and soles (IL 1 alpha/beta ratio greater than 700 in trunk and 5.4 in palms and soles) indicating a site-dependent difference in the excretion of the two IL 1 molecules. IL 1 concentration was high in spontaneous (IL 1 alpha, 3.7; IL 1 beta, 0.3 ng/mL) and pilocarpine induced sweat (IL 1 alpha, 3.9; IL 1 beta, 1.2 ng/mL), and it was much increased during jogging and sauna (IL 1 alpha, 22.6; IL 1 beta, 3.3 ng/mL). This does not appear to represent an excretory process aimed at clearing blood IL 1, but rather a stress-induced increased production of IL 1 by sweat gland cells.  相似文献   
9.
RJ 2.2.5 is a human B cell mutant, derived from Raji cells, which has lost expression of major histocompatibility complex (MHC) class II genes because of a defect in the AIR1 locus function. The MHC class II-positive phenotype can be restored by introducing an active AIR1 locus or its mouse equivalent, Air-1. An example of the latter is the H4 cell hybrid, derived by somatic cell fusion between RJ 2.2.5 and mouse class II-positive spleen cells. H4 contains a single mouse chromosome, autosome 16, in which the Air-1 locus maps, and an entire RJ 2.2.5-derived genome. In the present study we show that the physiologic target of the Air-1 locus product is contained within a limited HLA-DRA promoter sequence of 300 base pairs, encompassing the crucial Y, X, and W cis-acting elements. A plasmid construct, pDRA300neo, containing the HLA-DRA promoter sequence which drives the expression of the neomycin resistance gene, has been stably integrated in the genome of the H4 hybrid. Transfectants selected in the presence of G418 retain mouse chromosome 16 and express the DR genes. On the other hand, transfectants grown in a non-selective medium segregate mouse chromosome 16; this is accompanied by a loss of DRA gene expression and G418 resistance, although pDRA300neo is still integrated in the genome. These results offer scope for using this experimental model to clone the Air-1 gene in a straightforward way. Correspondence to: R. S. Accolla.  相似文献   
10.
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