全文获取类型
收费全文 | 208684篇 |
免费 | 13887篇 |
国内免费 | 1315篇 |
专业分类
耳鼻咽喉 | 2707篇 |
儿科学 | 4779篇 |
妇产科学 | 5003篇 |
基础医学 | 29949篇 |
口腔科学 | 3758篇 |
临床医学 | 21285篇 |
内科学 | 39256篇 |
皮肤病学 | 5320篇 |
神经病学 | 16884篇 |
特种医学 | 9008篇 |
外科学 | 26778篇 |
综合类 | 2544篇 |
现状与发展 | 6篇 |
一般理论 | 165篇 |
预防医学 | 16478篇 |
眼科学 | 5116篇 |
药学 | 16950篇 |
中国医学 | 1656篇 |
肿瘤学 | 16244篇 |
出版年
2023年 | 1471篇 |
2022年 | 3504篇 |
2021年 | 6546篇 |
2020年 | 3500篇 |
2019年 | 5291篇 |
2018年 | 6228篇 |
2017年 | 4632篇 |
2016年 | 5677篇 |
2015年 | 7202篇 |
2014年 | 9120篇 |
2013年 | 11259篇 |
2012年 | 16961篇 |
2011年 | 16521篇 |
2010年 | 9565篇 |
2009年 | 7995篇 |
2008年 | 12582篇 |
2007年 | 12394篇 |
2006年 | 11428篇 |
2005年 | 10818篇 |
2004年 | 9578篇 |
2003年 | 8255篇 |
2002年 | 7195篇 |
2001年 | 4581篇 |
2000年 | 4162篇 |
1999年 | 3473篇 |
1998年 | 1603篇 |
1997年 | 1203篇 |
1996年 | 1119篇 |
1995年 | 1015篇 |
1994年 | 862篇 |
1993年 | 737篇 |
1992年 | 1637篇 |
1991年 | 1613篇 |
1990年 | 1400篇 |
1989年 | 1284篇 |
1988年 | 1188篇 |
1987年 | 1055篇 |
1986年 | 1035篇 |
1985年 | 906篇 |
1984年 | 680篇 |
1983年 | 599篇 |
1982年 | 415篇 |
1981年 | 397篇 |
1980年 | 359篇 |
1979年 | 529篇 |
1978年 | 426篇 |
1977年 | 402篇 |
1976年 | 356篇 |
1974年 | 362篇 |
1973年 | 343篇 |
排序方式: 共有10000条查询结果,搜索用时 26 毫秒
31.
A discrete time optimal control for linear time-delay systems is developed to ensure that all closed-loop eigenvalues will lie inside a circular region centred at (β;, 0) with radius α. It is shown that by suitable manipulations the problem can be reduced to a standard discrete time quadratic regulator problem. An illustrative example is included to demonstrate the applicability of the proposed method. 相似文献
32.
Diarrhetic shellfish poisoning (DSP) is a serious and globally widespread phytoplankton-related seafood illness. Although DSP is rarely life-threatening, it causes incapacitating diarrhea and vomiting with no known medical treatments. In addition, phytoplankton producing DSP toxins have been identified in temperate coastal waters worldwide, and their numbers may be increasing as a result of coastal eutrophication. The toxic effects of the major DSP toxins, okadaic acid and dinophysistoxin-1 (35-methylokadaic acid), appear to originate from their inhibitory activity against a family of structurally related serine/threonine protein phosphatases (PSPases). In particular, the inhibition of essential PSPases (e.g. PP1 and PP2A) has catastrophic consequences in most eukaryotic cells. Exploiting the potent inhibitory property of the DSP toxins, we have developed an enzyme-based assay (PP2A assay) capable of detecting both okadaic acid and dinophysis- toxin-1 in nanogram amounts. The assay employs purified PP2A, which has an extremely high affinity for both DSP toxins. This provides the PP2A assay with a level of sensitivity comparable to, or surpassing, that of most monoclonal antibody probes. To evaluate the PP2A assay as a means of detecting contaminated shellfish, a series of spike recovery experiments was conducted. The findings from these studies suggest that the PP2A assay has the potential for development into a rapid and relatively simple method for detecting PSPase inhibitors in crude extracts produced from shellfish. 相似文献
33.
34.
Summary— KR31080 (2-butyl-5-methyl-6-(1-oxopyridin-2-yl)-3-[[2'-(1H-tetrazol-5-yl) biphenyl-4-yl]methyl]-3H-imidazo[4,5-b] pyridine) is a potent inhibitor of angiotensin type 1 (AT1 ) receptors in rabbit aorta and human recombinant AT1 receptors. In the isolated rabbit thoracic aorta, KR31080 caused a nonparallel shift to the right of the concentration-response curves to angiotensin II (All) with decreased maximal response (pD'2 = 10.1 ± 0.1), but had no effect on the contractile response induced by norepinephrine. KR31080 inhibited specific [125 I]AII binding to rabbit aortic membranes (AT, receptors) and [125 I][Sar1 , Ile8 ]AII binding to human recombinant AT1 receptors in a concentration-dependent manner with IC50 values of 0.84 ± 0.08 nM and 1.92 ± 0.15 nM, respectively, but did not inhibit specific [125 I)AII binding to bovine cerebellum membranes (ÀT2 receptors). In the Scatchard analysis, KR31080 interacted with rabbit aortic AT1 receptors in a competitive manner, similar to losartan. These results demonstrate that KR31080 is a potent and AT1 selective angiotensin receptor antagonist which exerts a competitive antagonism in the [125 I]AII binding assay and insurmountable AT1 receptor antagonism in the functional study. 相似文献
35.
OBJECTIVE: To determine the most frequent clinical causes of a prolonged activated partial thromboplastin time (APTT) result, and to determine whether a new heparin-removal device (the Hepchek, Pall Biomedical, Glen Cove, NY 11542) is capable of efficiently detecting the causes of these values. DESIGN: A combination of chart review and laboratory testing comparing the criterion standard--the heparin chromogenic substrate assay--with the Hepchek. Laboratory investigations were blinded and controlled. SETTING: Inpatient, acute-care hospital. PATIENTS: A total of 1,000 hospital patients with a variety of hemostatic disorders. MAIN OUTCOME MEASURE: The extent to which the Hepchek accurately identified the etiology of a prolonged APTT result. RESULTS: The APTT was prolonged in 25.2% of samples. The presence of heparin in the sample was confirmed by chromogenic assay or by using the Hepchek heparin-removal filter. The presence of heparin was confirmed in 12.8% of all samples and in more than 50% of all abnormal samples. The cause of the abnormal APTT was often unappreciated by the clinician. Bayesian analysis of the Hepchek's ability to diagnose heparin correctly as the cause of the abnormal APTT showed a sensitivity of 100% and specificity of 99.9%. CONCLUSION: Use of the Hepchek in the routine clinical laboratory is an efficient and rapid method of detecting heparin as a cause of isolated prolonged APTT results, and should reduce demands for unwarranted coagulation analyses and inappropriate treatment with blood products. 相似文献
36.
37.
Previously, we prepared two different monoclonal antibodies (mAbs) against human 4-1BB (CD137): an agonistic mAb BBK-1 and an antagonistic mAb BBK-2. In this paper, we describe the molecular cloning of these two mAbs and present comparisons of their amino acid sequences. cDNAs encoding the heavy (H) and light (L) chains of the two mAbs were cloned by screening of cDNA libraries constructed from hybridomas secreting these mAbs. Comparisons of amino acid sequences of the two mAbs showed that, while the constant regions of the H and L chains were identical between the two mAbs, the variable region showed 45% identity in H chains and 48% identity in L chains. This suggests that these two mAbs recognize different epitopes of 4-1BB and may have different effects on the activity of 4-1BB. 相似文献
38.
B Lu J M Lee R Elliott C F Dreyfus J E Adler I B Black 《Brain research. Molecular brain research》1991,11(3-4):359-362
Nerve growth factor (NGF) gene expression in central nervous system (CNS) glia appears to be associated with active glial growth. To study the underlying molecular mechanisms, we examined the effects of a number of growth-related factors on NGF mRNA expression in glial cultures. Our results suggest that glial membrane interaction, as a consequence of growth, actively inhibits NGF gene expression in CNS glia. 相似文献
39.
40.
Critical size defect in the canine mandible. 总被引:3,自引:0,他引:3
Jin-Young Huh Byung-Ho Choi Byung-Young Kim Seoung-Ho Lee Shi-Jiang Zhu Jae-Hyung Jung 《Oral surgery, oral medicine, oral pathology, oral radiology, and endodontics》2005,100(3):296-301
OBJECTIVE: The purpose of this study was to determine the minimum size defect in a canine mandible that would not spontaneously heal during the dog's natural life (the critical size defect). STUDY DESIGN: Sixteen adult female mongrel dogs underwent continuity resection on both sides of the mandible to create bilateral defects. In 8 dogs, mandibular defects ranging from 5 to 20 mm were created with periosteal resection. In the other 8 dogs, mandibular defects ranging from 30 to 60 mm were created preserving the periosteum. The dogs were then killed at 6 months and the defects examined using radiographs and histologic analysis. RESULTS: When the periosteum was removed, mandibular defects greater than 15 mm failed to heal across the entire defect. However, when the periosteum was preserved, mandibular defects needed to be greater than 50 mm in order to fail to heal. CONCLUSION: The critical size defect in a canine mandible model is 15 mm when the periosteum is removed and 50 mm when the periosteum is preserved. 相似文献