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   7889篇
  免费   668篇
  国内免费   205篇
耳鼻咽喉   16篇
儿科学   160篇
妇产科学   67篇
基础医学   922篇
口腔科学   76篇
临床医学   887篇
内科学   1293篇
皮肤病学   180篇
神经病学   356篇
特种医学   140篇
外科学   366篇
综合类   913篇
预防医学   383篇
眼科学   1718篇
药学   770篇
  4篇
中国医学   366篇
肿瘤学   145篇
  2024年   21篇
  2023年   124篇
  2022年   191篇
  2021年   369篇
  2020年   256篇
  2019年   248篇
  2018年   261篇
  2017年   282篇
  2016年   279篇
  2015年   287篇
  2014年   414篇
  2013年   428篇
  2012年   368篇
  2011年   423篇
  2010年   351篇
  2009年   256篇
  2008年   343篇
  2007年   349篇
  2006年   312篇
  2005年   262篇
  2004年   237篇
  2003年   271篇
  2002年   217篇
  2001年   158篇
  2000年   152篇
  1999年   184篇
  1998年   120篇
  1997年   134篇
  1996年   102篇
  1995年   100篇
  1994年   76篇
  1993年   78篇
  1992年   65篇
  1991年   62篇
  1990年   51篇
  1989年   57篇
  1988年   55篇
  1987年   31篇
  1986年   42篇
  1985年   119篇
  1984年   115篇
  1983年   96篇
  1982年   94篇
  1981年   91篇
  1980年   60篇
  1979年   47篇
  1978年   36篇
  1977年   27篇
  1976年   25篇
  1975年   9篇
排序方式: 共有8762条查询结果,搜索用时 31 毫秒
61.
杨霄  王克学 《医学信息》2007,20(11):990-992
目的观察血液回收技术对非体外循环冠状动脉旁路移植患者红细胞、血小板和血液粘度的影响。方法2005年8月~2007年10月间,共完成46例非体外循环冠状动脉旁路移植术,随机分为实验组(血液回收组)和对照组(不使用血液回收机组),每组23例。观察两组用血液制品的数量和术后24h的引流量,比较两组术前和术后24h的红细胞计数、血红蛋白、红细胞压积、血小板计数、低切全血粘度和高切全血粘度。结果实验组用浓缩红细胞和血浆的量明显少于对照组,两组术后24h引流量、术前和术后24h的红细胞计数、血红蛋白、红细胞压积、血小板计数、低切全血粘度和高切全血粘度之间的差异无显著性意义。结论血液回收技术在非体外循环冠状动脉旁路移植患者中能减少输血,对红细胞、血小板和血液粘度无不利影响。  相似文献   
62.
A recurrent cardiac myxoma is examined histochemical ly at the ultrastructural level. By routine electron microscopy the stellate “myxoma” cell exhibits features suggestive of a secretory function in synthesis of its myxoid stroma. Spicer's high iron diamine (HID), which stains specifically for sulfated glycoconjugates, is utilized for intracellular localization of glycosaminoglycans. HID-positive reactive sites are localized within the Golgi-derived vacuoles and secretory granules of the myxoma cells. No staining is obtained with other cytoplasmic organelles except rare secondary lyso-somes. Although colloidal iron is less specific, both intracellular and extracellular positive reactive sites are observed. With ruthenium red staining the proteoglycans in the extracellular stroma can be visualized as numerous positively stained, polygonal 250-500 A matrix granules with faint filamentous projections. Positive intracellular ruthenium red-stained granules are also observed within the Golgi-derived vacuoles. The alcianophilia of the myxoid stroma with Alcian blue is almost completely abolished by prior treatment with bovine testicular hyaluronidase but is unaffected by leech hyaluronidase, indicating chondroitin sulfates A and/or C, not hyaluronic acid, as the major biochemical constituents of the stroma and the observed extracellular matrix granules. The above findings provide cytochemical evidence of intracellular synthesis of sulfated glycosaminoglycans and proteoglycans of the myxoma cell and its active participation in production of its stroma.  相似文献   
63.
The Thy-1 antigens or rat brain and thymus have been isolated and chemically characterized, but those of mice have not been identified. Moreover, it is uncertain whether the antigens are glycolipids or glycoproteins. This study with highly purified preparations of gangliosides GM1, 1GD1a, GD1b and GT1b from bovine brain and several ganglioside fractions from mouse brain showed that Thy-1 activity does not reside in gangliosides, but rather in the chloroform-methanol-insoluble residue of brain remaining after extraction of gangliosides. The antigen could be solubilized from this residue with a non-ionic detergent. The antigenic activity of the solubilized preparation was heat-labile but resistant to periodate. The chemical properties of the Thy-1 antigen of mouse brain are discussed.  相似文献   
64.
 Three major ionic currents, Ca2+-dependent K+ current (I K-Ca), delayed rectifier type K+ current (I kd) and Ca2+ current (I Ca), were activated by depolarization under whole-cell clamp in single smooth muscle cells isolated from guinea-pig urinary bladder. Externally applied ruthenium red (RuR) reduced the amplitude of I K-Ca and I Ca at 0 mV (IC50 values were 4.2 and 5.6 μM, respectively), but did not affect I Kd. Spontaneous transient outward currents (STOCs) and caffeine-induced outward currents (I caf) at –30 mV were reduced by external 10 μM RuR. When 10 μM RuR was added to the pipette solution, I K-Ca during depolarization, STOCs and I caf significantly decreased with time. RuR did not change the unitary current amplitude of the large-conductance Ca2+-dependent K+ (BK) channels, but reduced the open probability of the channel under excised patch-clamp recording mode. RuR reduced the channel activity more effectively from the cytosolic face than from the other. This inhibition decreased when the cytosolic Ca2+ concentration was increased. These results indicate that RuR blocks BK and Ca2+ channels in urinary bladder smooth muscle cells. The decrease in I K-Ca, STOCs and I caf by RuR is attributable to the direct inhibition of BK channel activity, probably in addition to the inhibition of Ca2+ release from storage sites. The direct inhibition of BK channel activity by RuR may be related to the interaction of RuR with the Ca2+-binding sites of the channel protein. Received: 15 October 1997 / Received after revision and accepted: 25 November 1997  相似文献   
65.
The fractional volume occupied by lipofuscin granules in epithelial cells of the midgut or oenocytes of abdominal fat body of 3-day-old and 13-day-old male houseflies was determined in two groups of flies by electron microscopic morphometry. One group had developed from larvae reared on diets containing no added polyunsaturated fatty acids and the second from larvae reared on diets containing added linoleic acid. No polyunsaturated fatty acids could be detected in the lipids of the first group of flies using a method which would have detected their presence in amounts greater than 0.1% of the total esterified fatty acids. The second group contained at least two hundred times more than this minimal level. The volume of lipofuscin granules increased significantly (p less than 0.01) (about threefold for the fat body and twofold in midgut cells) between 3 days and 13 days of age but no statistically significant difference was seen between the two groups of flies at the same age. The results show that if lipofuscin formation depends on the oxidation of polyunsaturated fatty acids in the housefly, then extremely small amounts of the acids are involved which lie below the detection limit of the methods employed. The age-associated small increase of extractable fluorescence seen previously in the linoleic acid group of flies is not associated with an increase in the lipofuscin granules.  相似文献   
66.
We have characterized the early biosynthetic forms of the histidine-rich protein (HisRP), a major, granule-bound protein (Mr 58 000) of the avian malarial parasite Plasmodium lophurae. We have translated poly(A)-containing, size-selected parasite mRNA in the wheat germ cell-free system in the presence of [3H]histidine. HisRP was synthesized as a larger precursor (Mr 63 000). When dog pancreas microsomal membranes were present in the cell-free system during translation, a still larger form of HisRP (Mr 66 000) was detected. This larger form was segregated into the dog pancreas microsomal vesicles and was core glycosylated. Presumably, it corresponds to an intermediate form located in the parasite rough endoplasmic reticulum (RER). The difference in the Mr of approx. 8 000 between this RER associated 'pro' form and the granule-bound, mature form of HisRP suggests that proteolytic processing occurs upon transport from the RER to the granule. Segregation and core glycosylation were strictly coupled to translation and were not observed upon posttranslational addition of microsomal membranes. Thus, the early events in the biosynthesis of HisRP are similar to those established for secretory and lysosomal proteins.  相似文献   
67.
243例健康人血红细胞悬浮液射频介电特性的研究   总被引:8,自引:0,他引:8  
本文应用同轴传输线反射法建立的细胞悬浮液介电测量系统,测量了243例健康人(男120,女123名)血红细胞悬浮液在1~500MHz频率范围的介电常数和电导率。结果表明不同性别和不同血型之间的红细胞悬浮液的介电参数无显著差异。将19~80岁之间的受试者按10岁年龄间隔分成六个组,探讨年龄差别对介电参数的影响;发现50岁左右是人红细胞介电参数有显著差异的临界年龄,49岁后三个高年龄组的介电参数显著地低于49岁前的三个低年龄组的数值(P<0.05)。本文的结果证明年龄对人血红细胞的介电参数有明确的影响。  相似文献   
68.
A Coutinho  L Forni 《Immunobiology》1981,158(3):182-190
The enhancement of antibody responses by IgM antibodies administered with low doses of antigen has been studied in a T-dependent (SRBC) and an T-independent (alpha 1,6 dextran) system. It has been found that IgM anti-SRBC antibodies do not enhance a SRBC response in nude mice. The T-cell dependency was also directly demonstrated by showing the effect of IgM on T-cell priming in transfer experiments. The simultaneous injection of antigen and IgM antibody also induced a polyclonal increase of IgM, PFC, which was not due to a non-specific "adjuvant" effect of IgM, as we could not detect a similar effect on an ongoing response to HRBC in mice simultaneously given SRBC and IgM anti-SRBC antibodies. The specificity of the helper cell for either the antibody or the antigen was investigated in a response to alpha 1, 6 dextran, in which we could demonstrate antibody-specific helper T cells, but no antigen-specific help. We have found that IgM anti-dextran antibodies do not enhance and rather suppress the response of normal, high-responder mice, to dextran, suggesting that the T cells mediating the "19S enhancement" are antigen-specific. The magnitude of the enhancement response, as compared to the responses induced by either antigen or antibody alone, implies a synergistic mechanism, possibly involving antigen-specific and antibody(idiotype)-specific T helper cells.  相似文献   
69.
We have established stable, bright green fluorescent protein (GFP)- or red fluorescent protein (RFP)-expressing HT-1080 human fibrosarcoma clones. These cell lines showed similar cell proliferation rates and high-frequency experimental lung metastasis. The HT-1080-GFP and -RFP clones enable simultaneous real-time dual-color imaging in the live animal. HT-1080 cells were transduced with retroviral vectors containing GFP or RFP and the neomycin resistance gene. Stable transformants were selected stepwise with G418 up to 800 μl/ml. Subsequently, high GFP- or RFP-expressing clones, HT-1080-GFP or HT-1080-RFP, respectively, were selected. 3×106 cells from each clone were mixed and injected into the tail vein of SCID mice. The cells seeded the lung at high frequency with subsequent formation of pure green and pure red colonies as well as mixed yellow colonies with different patterns visualized directly on excised lungs. The lung metastases were also visualized by external fluorescence imaging in live animals through skin-flap windows over the chest wall. Lung metastases were observed on the lung surface of all mice. SCID mice well tolerated multiple surgical procedures for direct-view imaging via skin-flap windows. Real-time metastatic growth of the two different colored clones in the same lung was externally imaged with resolution and quantification of green, red, or yellow colonies in live animals. The color coding enabled determination of whether the colonies grew clonally or were seeded as a mixture with one cell type eventually dominating, or whether the colonies grew as a mixture. The simultaneous real-time dual-color imaging of metastatic colonies described in this report gives rise to the possibility of color-coded imaging of clones of cancer cells carrying various forms of gene of interest. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   
70.
BACKGROUND: To assess the release of placental growth factor (PlGF) into peritoneal fluid in women with and without endometriosis, we measured its concentration with reference to disease stage, the presence of red endometriotic lesions and the phase of menstrual cycle. METHODS: Surgery was scheduled in the proliferative or secretory phase of the menstrual cycle for 59 women with (n = 35) or without (n = 24) endometriosis. The latter group comprised women undergoing surgery for ovarian cystadenomas. PlGF concentrations in the peritoneal fluid were measured using an enzyme-linked immunosorbent assay. RESULTS: PlGF concentration in the peritoneal fluid was markedly elevated in the endometriosis patients (median 189 pg/ml, interquartile range 84-475 pg/ml) as compared with the controls (88 pg/ml, 41-213 pg/ml; P < 0.001), especially in women with red lesions. Significantly greater values during the secretory phase of the menstrual cycle as compared with the proliferative phase were observed in both the control (cystadenoma) group (P < 0.05) and the endometriosis group (P < 0.001). CONCLUSIONS: Our findings suggest that production of PlGF is sensitive to the cyclic changes in ovarian steroids and may contribute to the pathogenesis of endometriosis, especially that of red lesions, by promoting neovascularization.  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