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   14077篇
  免费   1077篇
  国内免费   39篇
耳鼻咽喉   170篇
儿科学   347篇
妇产科学   161篇
基础医学   1705篇
口腔科学   143篇
临床医学   1586篇
内科学   3254篇
皮肤病学   203篇
神经病学   1270篇
特种医学   467篇
外科学   2690篇
综合类   168篇
一般理论   16篇
预防医学   1015篇
眼科学   305篇
药学   809篇
中国医学   11篇
肿瘤学   873篇
  2024年   22篇
  2023年   182篇
  2022年   372篇
  2021年   796篇
  2020年   392篇
  2019年   594篇
  2018年   701篇
  2017年   446篇
  2016年   477篇
  2015年   548篇
  2014年   770篇
  2013年   840篇
  2012年   1328篇
  2011年   1317篇
  2010年   682篇
  2009年   561篇
  2008年   921篇
  2007年   864篇
  2006年   719篇
  2005年   624篇
  2004年   545篇
  2003年   464篇
  2002年   363篇
  2001年   48篇
  2000年   37篇
  1999年   44篇
  1998年   51篇
  1997年   38篇
  1996年   36篇
  1995年   23篇
  1994年   18篇
  1993年   25篇
  1992年   18篇
  1991年   20篇
  1990年   17篇
  1989年   22篇
  1988年   16篇
  1987年   19篇
  1986年   17篇
  1985年   25篇
  1984年   13篇
  1983年   11篇
  1982年   17篇
  1981年   19篇
  1980年   17篇
  1979年   23篇
  1978年   18篇
  1976年   13篇
  1975年   6篇
  1974年   6篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
61.
62.
Folding and assembly of MHC molecules in mammals occurs in the endoplasmic reticulum (ER), but has not been studied in teleosts. Calnexin (CNX) is an ER chaperone that associates with glycoproteins bearing a monoglucosylated N-linked oligosaccharide side chain. Here we report the first identification and characterization of a full-length CNX cDNA clone in a teleost, and the association of the CNX chaperone with MHC class II in a channel catfish T cell line. The 1.8 kb CNX clone encodes a protein of 607 amino acids that is 72% identical to the consensus sequence of mammalian CNXs. The association of CNX with class II is of particular interest because the native MHC class II alpha chain of Ictalurus punctatus does not bear any N-linked oligosaccharide consensus glycosylation sequences. Thus the assembly of class II molecules in the catfish probably proceeds via different steps than occurs in mammals.  相似文献   
63.
Summary Na pump current was measured in rat ventricular myocytes to determine if -adrenergic stimulation can directly modulate Na,K-ATPase activity. Enzymatically-isolated heart cells were voltage-clamped with a single patch electrode and Na pump current was briefly activated by rapidly increasing extracellular [K+] from 0 to 15 mM for 3–5 s after other ionic currents were blocked or inactivated. The salt solution in the voltage-clamping electrode included (in mM): (1) 100 Na+, 10 EGTA, (2) 5 Na+, 10 EGTA, or (3) 100 Na+, 7.5 Ca2+, 10 EGTA (free [Ca2+]=480 nM). With all three electrode solutions, Na pump current was not significantly changed after 2–4 min in the presence of 10 M isoprenaline. -adrenergic pathways were still intact as evidenced by the two-fold increase in Cd2+-sensitive Ba2+ current through calcium channels that was observed in the presence of isoprenaline. Thus, -adrenergic stimulation does not appear to directly regulate Na,K-ATPase activity in rat ventricular myocytes.  相似文献   
64.
Liver infiltrating lymphocytes (LIL) were isolated from HCV-positive (+) and HCV-negative (–) end-stage livers. Phenotypic analysis and functional studies using proliferative and lymphocytotoxic assays were performed with the isolated LIL. Two CD3+ lymphocyte populations were found in LIL using FITC anti-CD3 monoclonal antibodies (mAb). One was a bright fluorescence intensity population (as in PBL), and the other dim. We calculated the number of FITC-anti-CD3 mAbs bound per lymphocyte on PBL and LIL and found 80,040 ± 4628 and 39,615 ± 3932, respectively. Therefore, HCV+ and HCV– patient PBL contained approximately twice the number of CD3 molecules per cell than patient CD3+ LIL. LIL also contained approximately a threefold higher concentration of TCR+, CD4–CD8–, and CD56,16 (NK) cells than the patient PBL. Thus, a major subset of LIL is phenotypically similar to mouse NK1.1+ intermediate T cells. LIL freshly isolated from HCV+ livers exhibited weak CTL activity against EBV- or Con A-transformed lymphoblast targets infected with vaccinia–HCV recombinant virus (rHCV) or primary hepatocyte cultured cells. However, after in vitro coculture of LIL with rHCV, these cells developed a strong cytotoxicity for the above targets. In contrast, LIL from HCV– livers were not cytotoxic against the same targets. Histochemical studies (in situ) demonstrated that these hepatocytes express CD95, and stains demonstrated apoptosis. The HCV+ hepatocytes also express class I MHC molecules and ICAM-1. The addition of mAb specific for these adhesion molecules inhibited CML activity. Short-term cultured hepatocytes (targets) from HCV+ and HCV– patients produced low levels of cytokines IL-1, IL-2, IL-6, TNF, and IFN- but a high level of IL-8. It is speculated that LIL expressing reduced numbers of CD3 molecules may even function as immune regulators as proposed for intermediate T cells in mice.  相似文献   
65.
PURPOSE: To determine emergency medicine residents' emotional and behavioral responses to their medical errors and examine associations between residents' responses to medical error and perceptions of their training. METHOD: In 2003, 55 residents at two U.S. residency programs were asked to complete questionnaires about their errors and responses to their errors in three domains: emotional response, learning behavior, and disclosure. The questions were a mixture of free text, yes/no responses, and some were rated using a five-point Likert scale. Based on a conceptual framework, the authors constructed scales to describe the various domains and associations between the residents' responses to medical error and perceptions of their training were examined using Somers' D. RESULTS: A total of 43 residents returned questionnaires (80%); 40 of these residents described errors. Thirty-three (83%) residents discussed the error with someone; 27 (71%) with the attending and 10 (28%) with the patient/family. Negative emotions were common: 27 (68%) felt remorse, 21 (53%) guilt, 23 (58%) inadequacy, and 22 (55%) frustration. Residents' negative emotional responses were associated with their personal characteristics [26% (95% CI, 5-47%) association with lack of experience] and residents' perceptions of their training environment: 15% association with job overload (95% CI, -8-38%) and 23% association with lack of institutional support (95% CI, 5-41%). While 32 (81%) residents increased attention to detail, only 2 (5%) increased their use of evidence-based medicine. CONCLUSIONS: Errors committed by emergency medicine residents often resulted in negative emotions, limited constructive system-based improvements, and inadequate disclosure. Negative perceptions of the training environment are associated with negative emotional responses.  相似文献   
66.
Heme oxygenase-1 (HO-1) plays a key role in protecting tissue from oxidative stress. Although some studies implicate HO-1 in modulating thrombosis after vascular injury, the impact of HO-1 on the rate of clot formation in vivo is poorly defined. This study examined the potential function of HO-1 in regulating platelet-dependent arterial thrombosis. Platelet-rich thrombi were induced in C57BL/6J mice by applying 10% ferric chloride to the exposed carotid artery. Mean occlusion time of wild-type mice (n = 10) was 14.6 +/- 1.0 min versus 12.9 +/- 0.6 min for HO-1-/- mice (n = 11, p = 0.17). However, after challenge with hemin, mean occlusion time was significantly longer in wild-type mice (16.3 +/- 1.2 min, n = 15) than HO-1-/- mice (12.0 +/- 1.0 min, n = 9; p = 0.021). Hemin administration induced an approximately twofold increase in oxidative stress, measured as plasma thiobarbituric acid reactive substances. Immunohistochemical analysis revealed that hemin induced a robust increase in HO-1 expression within the carotid arterial wall. Ex vivo blood clotting within a collagen-coated perfusion chamber was studied to determine whether the accelerated thrombosis observed in HO-1-/- mice was contributed to by effects on the blood itself. Under basal conditions, mean clot formation during perfusion of blood over collagen did not differ between wild-type mice and HO-1-/- mice. However, after hemin challenge, mean clot formation was significantly increased in HO-1-/- mice compared with wild-type controls. These results suggest that, under basal conditions, HO-1 does not exert a significant effect on platelet-dependent clot formation in vivo. However, under conditions that stimulate HO-1 production, platelet-dependent thrombus formation is inhibited by HO-1. Enhanced HO-1 expression in response to oxidative stress may represent an adaptive response mechanism to down-regulate platelet activation under prothrombotic conditions.  相似文献   
67.
Five TLRs are thought to play an important role in antiviral immunity, sensing viral products and inducing IFN-alpha/beta and -lambda. Surprisingly, patients with a defect of IRAK-4, a critical kinase downstream from TLRs, are resistant to common viruses. We show here that IFN-alpha/beta and -lambda induction via TLR-7, TLR-8, and TLR-9 was abolished in IRAK-4-deficient blood cells. In contrast, IFN-alpha/beta and -lambda were induced normally by TLR-3 and TLR-4 agonists. Moreover, IFN-beta and -lambda were normally induced by TLR-3 agonists and viruses in IRAK-4-deficient fibroblasts. We further show that IFN-alpha/beta and -lambda production in response to 9 of 11 viruses tested was normal or weakly affected in IRAK-4-deficient blood cells. Thus, IRAK-4-deficient patients may control viral infections by TLR-3- and TLR-4-dependent and/or TLR-independent production of IFNs. The TLR-7-, TLR-8-, and TLR-9-dependent induction of IFN-alpha/beta and -lambda is strictly IRAK-4 dependent and paradoxically redundant for protective immunity to most viruses in humans.  相似文献   
68.
Immunosuppression, although necessary to enable the graft to escape the consequences of immune surveillance, carries some risks for the patient. There is an associated increase in neoplasms, opportunistic infections and end-organ toxicity. In addition, even with excellent patient compliance, rejection (acute and chronic) remains a major limitation that contributes to the loss or decrease in the function of the allograft. New drugs have been added to the armamentarium of immunosuppressive agents to suppress allograft rejection and to rescue grafts from cyclosporin-resistant rejection. With the availability of these immunosuppressive agents, it has become increasingly difficult to choose the appropriate combination of immunosuppressants with a beneficial effect for the patient and for the allograft. We describe 2 new immunosuppressive agents and some of their different uses in solid organ transplantation.  相似文献   
69.
70.
Leukodystrophies are a heterogeneous group of heritable disorders characterized by abnormal brain white matter signal on magnetic resonance imaging (MRI) and primary involvement of the cellular components of myelin. Previous estimates suggest the incidence of leukodystrophies as a whole to be 1 in 7,000 individuals, however the frequency of specific diagnoses relative to others has not been described. Next generation sequencing approaches offer the opportunity to redefine our understanding of the relative frequency of different leukodystrophies. We assessed the relative frequency of all 30 leukodystrophies (associated with 55 genes) in more than 49,000 exomes. We identified a relatively high frequency of disorders previously thought of as very rare, including Aicardi Goutières Syndrome, TUBB4A‐related leukodystrophy, Peroxisomal biogenesis disorders, POLR3‐related Leukodystrophy, Vanishing White Matter, and Pelizaeus‐Merzbacher Disease. Despite the relative frequency of these conditions, carrier‐screening laboratories regularly test only 20 of the 55 leukodystrophy‐related genes, and do not test at all, or test only one or a few, genes for some of the higher frequency disorders. Relative frequency of leukodystrophies previously considered very rare suggests these disorders may benefit from expanded carrier screening.  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