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   1517篇
  免费   76篇
  1593篇
  2022年   11篇
  2021年   26篇
  2020年   3篇
  2019年   24篇
  2018年   13篇
  2017年   12篇
  2016年   32篇
  2015年   45篇
  2014年   71篇
  2013年   71篇
  2012年   108篇
  2011年   100篇
  2010年   56篇
  2009年   50篇
  2008年   125篇
  2007年   91篇
  2006年   92篇
  2005年   90篇
  2004年   106篇
  2003年   99篇
  2002年   105篇
  2001年   11篇
  2000年   9篇
  1999年   19篇
  1998年   25篇
  1997年   14篇
  1996年   12篇
  1995年   15篇
  1994年   15篇
  1993年   15篇
  1992年   9篇
  1991年   10篇
  1990年   6篇
  1989年   8篇
  1988年   9篇
  1987年   6篇
  1986年   3篇
  1985年   6篇
  1984年   4篇
  1983年   11篇
  1982年   12篇
  1981年   7篇
  1980年   7篇
  1979年   7篇
  1978年   2篇
  1977年   4篇
  1975年   3篇
  1974年   3篇
  1972年   2篇
  1971年   2篇
排序方式: 共有1593条查询结果,搜索用时 15 毫秒
31.
A cell line, designated NOCC, was established from the ascites of a patient with clear cell adenocarcinoma of the ovary. The cell line has been grown without interruption and continuously propagated by serial passaging (more than 76 times) over 7 years. The cells are spherical to polygonal-shaped, display neoplastic, and pleomorphic features, and grow in a jigsaw puzzle-like pattern while forming monolayers without contact inhibition. The cells proliferate rapidly, but are easily floated as a cell sheet. The population doubling time is about 29 h. The number of chromosomes ranges from 60 to 83. The modal number of chromosomes is 70–74 at the 30th passage. NOCC cells secreted 750.5 ng/ml of VEGF over 3 days of culture. Hypoxia inducible factor-1α (HIF-1α) is a primary regulator of VEGF under hypoxic conditions. NOCC cells were not sensitive to the anticancer drugs BEV, DOX, GEM, ETP, CDDP, or TXT. The graft of NOCC cells to a scid mouse displayed similar histological aspects to the original tumor. Both the NOCC cells and the graft of the NOCC cells gave a positive PAS reaction.  相似文献   
32.
Light-Induced CREB Phosphorylation and Gene Expression in Rat Retinal Cells   总被引:1,自引:0,他引:1  
Abstract: The signal pathway for light-induced expression of c- fos and the neuropeptide somatostatin (SS) in rat retinal cells was investigated. Flashing light induced c- fos and SS mRNA in the inner nuclear layer and the ganglion cell layer. As both c- fos and SS genes have a cyclic AMP response element (CRE) in their promoters, CRE-binding protein (CREB) phosphorylation in retinal cells was examined with a phospho-CREB-specific antibody. Both flashing light and administration of the L-type Ca2+ channel activator Bay K 8644 induced phosphorylation of CREB in the nuclei of the amacrine cells and the ganglion cells where c- fos /SS mRNAs were expressed. These cells could be double-stained with anti-calmodulin kinase II (anti-CaM kinase II) monoclonal antibody and phospho-CREB-specific polyclonal antiserum after Bay K 8644 administration, indicating the colocalization of phosphorylated CREB at Ser133 and CaM kinase II in the neural retina.  相似文献   
33.
34.
As a first step to elucidate the involvement of calmodulin in Ca2+-dependent regulation of ciliary motility, molecular species and properties of calmodulin-binding proteins (CaMBPs) in Tetrahymena cilia were investigated by a modified [125I]calmodulin overlay method. At least 36 kinds of CaMBPs were detected. All the CaMBPs bound to calmodulin in Ca2+-dependent and calmodulin-specific manners, but they showed different Ca2+-dependencies. Several of CaMBPs bound to calmodulin in the presence of 100 microM trifluoperazine, several did in the presence of 8 M urea, and a few of them were highly sensitive to trypsin digestion. Among these CaMBPs, we noticed a 95 000-dalton (D) CaMBP present in the outerdoublet microtubule fraction, which possessed some attributes of the calmodulin counterpart suggested from the results of our previous paper [12]. We discussed a possibility that this protein might correspond to one of the protein components of the interdoublet link.  相似文献   
35.
Abstract: The characteristics of β-alanine transport at the blood-brain barrier were studied by using primary cultured bovine brain capillary endothelial cells. Kinetic analysis of the β-[3H]alanine transport indicated that the transporter for β-alanine functions with Kt of 25.3 ± 2.5 µ M and J max of 6.90 ± 0.48 nmol/30 min/mg of protein in the brain capillary endothelial cells. β-[3H]Alanine uptake is mediated by an active transporter, because metabolic inhibitors (2,4-dinitrophenol and NaN3) and low temperature reduced the uptake significantly. Furthermore, the uptake of β-[3H]alanine required Na+ and Cl in the external medium. Stoichiometric analysis of the transport demonstrated that two sodium ions and one chloride ion are associated with one β-alanine molecule. The Na+ and Cl-dependent uptake of β-[3H]alanine was stimulated by a valinomycin-induced inside-negative K+-diffusion potential. β-Amino acids (β-alanine, taurine, and hypotaurine) inhibited strongly the uptake of β-[3H]alanine, whereas α- and γ-amino acids had little or no inhibitory effect. In ATP-depleted cells, the uptake of β-[3H]alanine was stimulated by preloading of β-alanine or taurine but not l -leucine. These results show that β-alanine is taken up by brain capillary endothelial cells, via the secondary active transport mechanism that is common to β-amino acids.  相似文献   
36.

Background

Video-assisted thoracic surgery (VATS) plays an important role in thoracic surgery because it is less invasive. However, the existence of severe pleural adhesions may make VATS difficult and complicated. The aim of this study was to assess the utility of inspiration and expiration computed tomography (respiratory dynamic CT (RD-CT)) in evaluation of pleural adhesions preoperatively.

Methods

RD-CT was performed on 107 patients undergoing thoracotomies (both VATS and open). We assessed synchronous motion during respiration on RD-CT. Comparing the results of RD-CT and intraoperative findings, we assessed the utility of preoperative evaluation.

Results

A negative correlation between sliding score and adhesion grade was revealed. Sliding score in adhesion negative patients was significantly higher than that in adhesion positive patients (P?<?0.0001). The sensitivity of RD-CT was 63.6%, specificity was 74.1%, and accuracy was 72%. Among 62 patients with a CT-Respiration Ratio of less than 0.65, the sensitivity of RD-CT was 77.8%, specificity was 86.8%, and accuracy was 85.5%.

Conclusions

RD-CT may be clinically useful for detecting the presence of pleural adhesions. It can be adopted as one of the criteria for deciding the surgical approach.
  相似文献   
37.
The reaction to C-banding was investigated throughout the mitotic cycle ofCrepis capillaris (2n=6): (1) 18–22 C-bodies or C-bands were found during mid telophase and interphase to prophase and metaphase, and also 12–14 at late anaphase to early telophase in the mitotic cycle. Fewer C-bands in late anaphase to early telophase were due to the absence of minute bands; (2) large and medium sized C-bands were strongly stained by Giemsa, while small and minute bands stained palely. It is suggested that inCrepis capillaris the difference of color in C-banded segments following Giemsa staining is referable to the amount of constitutive heterochromatin rather than to the difference in the condensation and decondensation; (3) the size of C-bodies changed during telophase to interphase and prophase. It is inferred that the extent of C-bodies is regulated by both the length of DNA sequences of constitutive heterochromatin and the amount of proteins combined with C-banded DNA. It was shown that the reaction to C-banding is neither due to the differential condensation of chromatin nor to a higher concentration of DNA in the C-banded regions, in the C-banding mechanism as has been suggested so far at least.  相似文献   
38.
Ohmuro J  Mogami Y  Baba SA 《Zoological science》2004,21(11):1099-1108
Transition from immotile to motile flagella may involve a series of states, in which some of regulatory mechanisms underlying normal flagellar movement are working with others being still suppressed. To address ourselves to the study of starting transients of flagella, we analyzed flagellar movement of sea urchin sperm whose motility initiation had been retarded in an experimental solution, so that we could capture the instance at which individual spermatozoa began their flagellar beating. Initially straight and immotile flagella began to shiver at low amplitude, then propagated exclusively the principal bend (P bend), and finally started stable flagellar beating. The site of generation of the P bend in the P-bend propagating stage varied in position in the basal region up to 10 microm from the base, indicating that the ability of autonomous bend generation is not exclusively possessed by the very basal region but can be unmasked throughout a wider region when the reverse bend (R bend) is suppressed. The rate of change in the shear angle, the curvature of the R bend and the frequency and regularity of beating substantially increased upon transition from P-bend propagating to full-beating, while the propagation velocity of bends remained unchanged. These findings indicate that artificially delayed motility initiation may accompany sequential modification of the motile system and that mechanisms underlying flagellar motility can be analyzed separately under experimentally retarded conditions.  相似文献   
39.
The design, synthesis, and SAR of a series of substituted spirohydantoins are described. Optimization of an in-house screening hit gave compounds that exhibited potent binding affinity and functional activity at MCH-R1.  相似文献   
40.
Several reports have documented a better prognosis for HIV‐1‐infected patients co‐infected with GBV‐C, while other reports have contradicted such findings with the result that this issue remains controversial. We attempted to clarify the complicated status of the effect of GBV‐C co‐infection on HIV‐1‐infected patients. GBV‐C RNA was detected in 37 samples in 182 HIV‐1‐infected patients (20.3%) using RT/nested PCR. Of these, 3 were determined to be GBV‐C genotype 1, 12 were genotype 2, and the remaining 22 were genotype 3. The GBV‐C viral load quantified by real‐time PCR ranged from 7.8 × 103 to 3.3 × 106 copies/ml. Weakly negative correlation was observed between GBV‐C viral load and HIV‐1 viral load in 19 HAART‐naïve patients, indicating that a higher GBV‐C viral load is associated with a greater suppression of HIV‐1 replication. A previously published in vitro study suggested that GBV‐C infection would induce up‐regulation of RANTES, leading to suppression of HIV‐1 replication. However, in our present study, the blood RANTES level was significantly lower in the GBV‐C co‐infected group than in the uninfected group (190–9,959 vs. 264–31,038 pg/ml, P=0.004). Our results suggested that a suppression of HIV‐1 replication by GBV‐C co‐infection is not mediated by up‐regulated RANTES, and thus call for another as yet unknown factor.  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