全文获取类型
收费全文 | 7966篇 |
免费 | 492篇 |
国内免费 | 291篇 |
专业分类
8749篇 |
出版年
2023年 | 151篇 |
2022年 | 256篇 |
2021年 | 239篇 |
2020年 | 235篇 |
2019年 | 319篇 |
2018年 | 310篇 |
2017年 | 213篇 |
2016年 | 214篇 |
2015年 | 260篇 |
2014年 | 464篇 |
2013年 | 607篇 |
2012年 | 364篇 |
2011年 | 461篇 |
2010年 | 342篇 |
2009年 | 367篇 |
2008年 | 371篇 |
2007年 | 375篇 |
2006年 | 336篇 |
2005年 | 322篇 |
2004年 | 307篇 |
2003年 | 248篇 |
2002年 | 226篇 |
2001年 | 138篇 |
2000年 | 108篇 |
1999年 | 109篇 |
1998年 | 97篇 |
1997年 | 92篇 |
1996年 | 92篇 |
1995年 | 73篇 |
1994年 | 68篇 |
1993年 | 62篇 |
1992年 | 53篇 |
1991年 | 60篇 |
1990年 | 48篇 |
1989年 | 43篇 |
1988年 | 27篇 |
1987年 | 23篇 |
1985年 | 56篇 |
1984年 | 85篇 |
1983年 | 55篇 |
1982年 | 87篇 |
1981年 | 64篇 |
1980年 | 46篇 |
1979年 | 48篇 |
1978年 | 39篇 |
1977年 | 39篇 |
1976年 | 30篇 |
1975年 | 28篇 |
1974年 | 21篇 |
1973年 | 27篇 |
排序方式: 共有8749条查询结果,搜索用时 15 毫秒
51.
52.
53.
54.
7alpha-Hydroxy-dehydroepiandrosterone and its 7beta-hydroxyepimer, which act as local immunomodulatory agents, dehydroepiandrosterone, cortisol, and major androgens, together with four cytokines-interleukins 2, 4, 10, and IFN-gamma, reflecting the activity of TH1 or TH2 cells present in semen, were measured in seminal plasma from 35 male donors. Cortisol, dehydroepiandrosterone, its sulfate, 7-hydroxy-dehydroepiandrosterone epimers, testosterone, and estradiol were also measured in their blood serum. Steroids and interleukins in semen as well as serum steroids and seminal interleukins were mutually correlated to find out whether a relationship between immunomodulatory steroids and cytokines influencing the immune environment does exist. A highly significant (P<0.001) positive correlation was found between seminal 7beta-hydroxy-dehydroepiandrosterone and IFN-gamma, while a negative correlation was found between cortisol and IL-10. Highly significant positive correlations were also found between serum 7alpha-hydroxy-dehydroepiandrosterone and seminal IFN-gamma and between serum 7beta-hydroxy-dehydroepiandrosterone and seminal IL-2, while a negative correlation was found between serum dehydroepiandrosterone and seminal IL-10. Different and in some instances, even contradictory findings concerning the influence of dehydroepiandrosterone and cortisol on TH1 and TH2 cytokines were observed in seminal plasma as compared to those found by others in serum. The differences can be ascribed to the different environments of mucosal and systemic immunity. Correlations between the levels of steroids and cytokines in seminal plasma did not always correspond to the correlations between given cytokines and hormones in sera. The results, however, are in agreement with our recent finding of an autonomous production of these steroids in the male reproductive tract. 相似文献
55.
A convenient synthesis of [1-14C]-mono-trans fatty acid using olefin inversion as a key-step is described. This methodology allows for a facile synthesis of [1-14C]-labelled mono-trans analogues of oleic, linoleic and linolenic acids. As an example, only eleven steps were necessary to obtain the [1-14C]-mono-E isomers of linolenic acid from its commercial all-Z form. In the first step, Barton's decarboxylation procedure yielded a bromo intermediate. Epoxidation of this compound resulted in the formation of three monoepoxides, which could be separated by HPLC. After identification by 1H NMR and MS, the pure monoepoxides were then subjected to inversion consisting of a stereospecific deoxygenation followed by a beta-elimination step. Finally, the labelling was introduced by substitution of the bromine by a [14C]-cyano group followed by hydrolysis. 相似文献
56.
Plasmacytoid dendritic cells (pDCs) represent a unique and crucial immune cell population capable of producing large amounts
of type I interferons (IFNs) in response to viral infection. The function of pDCs as the professional type I IFN-producing
cells is linked to their selective expression of Toll-like receptor 7 (TLR7) and TLR9, which sense viral nucleic acids within
the endosomal compartments. Type I IFNs produced by pDCs not only directly inhibit viral replication but also play an essential
role in linking the innate and adaptive immune system. The aberrant activation of pDCs by self nucleic acids through TLR signaling
and the ongoing production of type I IFNs do occur in some autoimmune diseases. Therefore, pDC may serve as an attractive
target for therapeutic manipulations of the immune system to treat viral infectious diseases and autoimmune diseases. 相似文献
57.
Possibilities of the linear-polarized infrared (IR-LD) spectroscopy of oriented colloid suspensions in nematic liquid crystals, for structural and local structural elucidation for first time are demonstrated of inorganic compounds and glasses. The advantages of the method for tellurite and borate glasses are shown. The IR-band assignment of the typical local structural units in the glasses are proposed by a comparison with the IR-characteristics of appropriate crystalline analogues as α-TeO2, V2O5, MoO3 · H2O and its high temperature form. The IR-spectroscopic characteristics of BO3, BO4 and boroxol ring are elucidated, using crystalline β-BaB2O4, SrB4O7, H3BO3 and B2O3 as model systems, where the structural moieties have been refined by single crystal X-ray diffraction. 相似文献
58.
Increased nonsterol isoprenoids, dolichol and ubiquinone, in the Smith-Lemli-Opitz syndrome: effects of dietary cholesterol 总被引:1,自引:0,他引:1
Pappu AS Connor WE Merkens LS Jordan JM Penfield JA Illingworth DR Steiner RD 《Journal of lipid research》2006,47(12):2789-2798
Smith-Lemli-Opitz syndrome (SLOS) is an inherited autosomal recessive cholesterol deficiency disorder. Our studies have shown that in SLOS children, urinary mevalonate excretion is normal and reflects hepatic HMG-CoA reductase activity but not ultimate sterol synthesis. Hence, we hypothesized that in SLOS there may be increased diversion of mevalonate to nonsterol isoprenoid synthesis. To test our hypothesis, we measured urinary dolichol and ubiquinone, two nonsterol isoprenoids, in 16 children with SLOS and 15 controls, all fed a low-cholesterol diet. The urinary excretion of both dolichol (P < 0.002) and ubiquinone (P < 0.02) in SLOS children was 7-fold higher than in control children, whereas mevalonate excretion was comparable. In a subset of 12 SLOS children, a high-cholesterol diet decreased urinary mevalonate excretion by 61% (P < 0.001), dolichol by 70% (P < 0.001), and ubiquinone by 67% (P < 0.03). Our hypothesis that in SLOS children, normal urinary mevalonate excretion results from increased diversion of mevalonate into the production of nonsterol isoprenoids is supported. Dietary cholesterol supplementation reduced urinary mevalonate and nonsterol isoprenoid excretion but did not change the relative ratios of their excretion. Therefore, in SLOS, a secondary peripheral regulation of isoprenoid synthesis may be stimulated. 相似文献
59.
Eun Young Kim Naghmeh Hassanzadeh Khayyat Stuart E. Dryer 《生物化学与生物物理学报:疾病的分子基础》2018,1864(10):3527-3536
The soluble urokinase receptor (suPAR) has been implicated in the pathogenesis of chronic kidney diseases (CKD) and may function as a circulating “permeability factor” driving primary focal and segmental glomerulosclerosis (FSGS). Here we examined the mechanisms whereby suPAR causes mobilization and increased activation of Ca2+-permeable TRPC6 channels, which are also implicated in FSGS. Treatment of immortalized mouse podocytes with recombinant suPAR for 24?h caused a marked increase in cytosolic reactive oxygen species (ROS) that required signaling through integrins. This effect was associated with increased assembly of active cell surface NADPH oxidase 2 (Nox2) complexes and was blocked by the Nox2 inhibitor apoycynin. Treatment with suPAR also evoked a functionally measurable increase in TRPC6 channels that was blocked by concurrent treatment with the ROS-quencher TEMPOL as well as by inhibition of Rac1, an essential component of active Nox2 complexes. Elevated ROS evoked by exposing cells to suPAR or H2O2 caused a marked increase in the abundance of tyrosine-phosphorylated proteins including Src, and suPAR-evoked Src activation was blocked by TEMPOL. Moreover, mobilization and increased activation of TRPC6 by suPAR or H2O2 was blocked by concurrent exposure to PP2, an inhibitor of Src family tyrosine kinases. These data suggest that suPAR induces oxidative stress in podocytes that in turn drives signaling through Src family kinases to upregulate TRPC6 channels. The combination of oxidative stress and altered Ca2+ signaling may contribute to loss of podocytes and progression of various forms of CKD. 相似文献
60.
Ying Wang Yunjing Zhang Xinwan Su Qiongzi Qiu Yuan Yuan Chunhua Weng Sailan Zou Yan Tian Weidong Han Pengyuan Liu Xingyi Guo Jianhua Mao Xianghui Fu Ping Wang Weiqiang Lin 《International journal of biological sciences》2022,18(4):1491
Clear cell renal cell carcinoma (ccRCC) is a primary kidney cancer with high aggressive phenotype and extremely poor prognosis. Accumulating evidence suggests that circular RNAs (circRNAs) play pivotal roles in the occurrence and development of various human cancers. However, the expression, clinical significance and regulatory role of circRNAs in ccRCC remain largely unclear. Here we report that circDVL1 to be reduced in the serums and tissues from ccRCC patients, and to negatively correlate with ccRCC malignant features. Overexpression of circDVL1 inhibits proliferation, induces G1/S arrest, triggers apoptosis, and reduces migration and invasion in different ccRCC cells in vitro. Correspondingly, circDVL1 overexpression suppresses ccRCC tumorigenicity in a mouse xenograft model. Mechanistically, circDVL1 serves as a sponge for oncogenic miR-412-3p, thereby preventing miR-412-3p-mediated repression of its target protocadherin 7 (PCDH7) in ccRCC cells. Collectively, our results demonstrate that circDVL1 exerts tumor-suppressive function during ccRCC progression through circDVL1/miR-412-3p/PCDH7 axis, and suggest that circDVL1 could be a novel diagnostic and prognositc marker and therapeutic target for ccRCC. 相似文献