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   644篇
  免费   27篇
  国内免费   2篇
  2022年   7篇
  2021年   13篇
  2020年   6篇
  2019年   11篇
  2018年   13篇
  2017年   6篇
  2016年   16篇
  2015年   17篇
  2014年   23篇
  2013年   40篇
  2012年   44篇
  2011年   39篇
  2010年   25篇
  2009年   21篇
  2008年   34篇
  2007年   41篇
  2006年   30篇
  2005年   28篇
  2004年   35篇
  2003年   32篇
  2002年   24篇
  2001年   6篇
  2000年   15篇
  1999年   12篇
  1998年   5篇
  1997年   7篇
  1996年   6篇
  1995年   8篇
  1994年   10篇
  1993年   8篇
  1992年   14篇
  1991年   7篇
  1990年   4篇
  1989年   4篇
  1988年   10篇
  1987年   3篇
  1986年   6篇
  1984年   5篇
  1982年   3篇
  1980年   3篇
  1979年   3篇
  1977年   7篇
  1976年   3篇
  1975年   2篇
  1974年   2篇
  1971年   3篇
  1970年   1篇
  1969年   1篇
  1967年   2篇
  1965年   2篇
排序方式: 共有673条查询结果,搜索用时 15 毫秒
61.
The light intermediate chains (LICs) of cytoplasmic dynein consist of multiple isoforms, which undergo post-translational modification to produce a large number of species separable by two-dimensional electrophoresis and which we have proposed to represent at least two gene products. Recently, we demonstrated the first known function for the LICs: binding to the centrosomal protein, pericentrin, which represents a novel, non-dynactin-based cargo-binding mechanism. Here we report the cloning of rat LIC1, which is approximately 75% homologous to rat LIC2 and also contains a P-loop consensus sequence. We compared LIC1 and LIC2 for the ability to interact with pericentrin, and found that only LIC1 will bind. A functional P-loop sequence is not required for this interaction. We have mapped the interaction to the central region of both LIC1 and pericentrin. Using recombinant LICs, we found that they form homooligomers, but not heterooligomers, and exhibit mutually exclusive binding to the heavy chain. Additionally, overexpressed pericentrin is seen to interact with endogenous LIC1 exclusively. Together these results demonstrate the existence of two subclasses of cytoplasmic dynein: LIC1-containing dynein, and LIC2-containing dynein, only the former of which is involved in pericentrin association with dynein.  相似文献   
62.
Steroid sulphatases regulate the formation of oestrogenic steroids which can support the growth of endocrine-dependent breast tumours. The development of potent steroid sulphatase inhibitors could therefore have considerable therapeutic potential. Several such inhibitors have now been developed of which the most potent to date is oestrone-3-O-sulphamate (EMATE). Unexpectedly, this inhibitor proved to be a potent oestrogen. In an attempt to reduce the oestrogenicity, whilst retaining the potent sulphatase inhibitory properties associated with this type of molecule, a number of A-ring modified derivatives were designed and synthesized. A-ring modified compounds included the 2-methoxy, 2/4-nitro, 2/4-n-propyl and 2/4-allyl EMATE analogues. The ability of these derivatives to inhibit oestrone sulphatase activity was examined using placental microsomes. The allyl-substituted EMATE derivatives were more potent inhibitors than the propyl analogues but were all considerably less potent than EMATE. In contrast, the 2-methoxy and 2/4-nitro analogues were potent sulphatase inhibitors with 4-nitro EMATE being 5 times more active than EMATE. The 4-nitro, 2-methoxy, 4-n-propyl and 4-allyl derivatives were also tested in vivo for their oestrogenicity and ability to inhibit sulphatase activity. While both 4-nitro and 2-methoxy EMATE were potent inhibitors in vivo, 2-methoxy EMATE had no stimulatory effect on uterine growth in ovariectomized rats. The identification of a potent steroid sulphatase inhibitor lacking any oestrogenicity, such as 2-methoxy EMATE, should be of considerable value in evaluating the potential of steroid sulphatase inhibition for breast cancer therapy.  相似文献   
63.
The Ranibizumab for the Treatment of Choroidal Neovascularisation (CNV) Secondary to Pathological Myopia (PM): an Individualized Regimen (REPAIR) trial was a prospective study exploring the efficacy and safety of intravitreal ranibizumab 0.5 mg using an individualized treatment regimen over 12 months. The current study investigated the impact of treatment with ranibizumab as needed (pro re nata [PRN]) on individuals with myopic choroidal neovascularization (mCNV) in the REPAIR study, using patient-reported outcome measures (PROMs) for treatment satisfaction and well-being. This study included 65 adults with mCNV and a best-corrected visual acuity (BCVA) letter score of 24–78 in the study eye. Patients completed the Macular Disease Treatment Satisfaction Questionnaire (MacTSQ) at months 1, 6 and 12, and the 12-item Well-Being Questionnaire (W-BQ12) at baseline and months 1, 6 and 12. Subgroup analyses investigated the relationship between PROM scores and treatment in the better- or worse-seeing eye (BSE/WSE), number of injections received, baseline BCVA, BCVA improvement and age. Pearson correlations between change in BCVA, MacTSQ scores and W-BQ12 scores were calculated. The main outcome measures were treatment satisfaction measured with the MacTSQ (score 0–72) and well-being measured with the W-BQ12 (score 0–36). Treatment satisfaction significantly increased over the study period (p = 0.0001). Mean MacTSQ scores increased by 9.7 and 10.0 in patients treated in their WSE and BSE, respectively. Treatment satisfaction was highest in individuals receiving only one injection at month 1; however, by month 12, scores were similar across injection subgroups. Patients aged 68 years or older had the highest MacTSQ scores. Well-being scores also significantly increased over the study period (p = 0.03). Mean W-BQ12 scores increased by 1.7 in patients treated in their WSE and by 2.1 in patients treated in their BSE. Individuals aged 40 years or younger had the greatest increases in general well-being. Patients who experienced stable or improved BCVA at month 12 had greater increases in W-BQ12 scores than those who experienced a decrease. Correlations between BCVA, MacTSQ scores and W-BQ12 scores were largely non-significant. In conclusion, treatment satisfaction and well-being increased during treatment with ranibizumab PRN. Although directly comparable data are limited for the MacTSQ and W-BQ12 in mCNV, these results complement PROM outcomes reported in related studies.  相似文献   
64.
Ectromelia virus (ECTV) causes mousepox in mice, a disease very similar to smallpox in humans. ECTV and variola virus (VARV), the agent of smallpox, are closely related orthopoxviruses. Mousepox is an excellent small animal model to study the genetic and immunologic basis for resistance and susceptibility of humans to smallpox. Resistance to mousepox is dependent on a strong polarized type 1 immune response, associated with robust natural killer (NK) cell, cytotoxic T lymphocyte (CTL) and gamma interferon (IFN-γ) responses. In contrast, ECTV-susceptible mice generate a type 2 response, associated with weak NK cell, CTL and IFN-γ responses but robust IL-4 responses. Nonetheless, susceptible strains infected with mutant ECTV lacking virus-encoded IFN-γ binding protein (vIFN-γbp) (ECTV-IFN-γbpΔ) control virus replication through generation of type 1 response. Since the IL-4/IL-13/STAT-6 signaling pathways polarize type 2/T helper 2 (Th2) responses with a corresponding suppression of IFN-γ production, we investigated whether the combined absence of vIFN-γbp, and one or more host genes involved in Th2 response development, influence generation of protective immunity. Most mutant mouse strains infected with wild-type (WT) virus succumbed to disease more rapidly than WT animals. Conversely, the disease outcome was significantly improved in WT mice infected with ECTV-IFN-γbpΔ but absence of IL-4/IL-13/STAT-6 signaling pathways did not provide any added advantage. Deficiency in IL-13 or STAT-6 resulted in defective CTL responses, higher mortality rates and accelerated deaths. Deficiencies in IL-4/IL-13/STAT-6 signaling pathways significantly reduced the numbers of IFN-γ producing CD4 and CD8 T cells, indicating an absence of a switch to a Th1-like response. Factors contributing to susceptibility or resistance to mousepox are far more complex than a balance between Th1 and Th2 responses.  相似文献   
65.
66.
67.
The present study was carried out to determine the accumulation and variation of trace elements in roots and leaves of Asparagus racemosus collected from four different altitudes in Uttarakhand, India, by atomic absorption spectroscopy. The metals investigated were Zn, Cu, Mn, Fe, Co, Na, K, Ca, and Li. The concentration level of Fe was found to be highest at an altitude of 2,250 m, whereas the level of Cu was lowest. The maximum concentrations of Zn, Cu, Mn, Fe, Co, Na, K, Ca, and Li were found to be 165.0?±?3.2, 34.0?±?0.5, 84.0?±?0.7, 2,040.0?±?0.3, 122.0?±?1.5, 745.0?±?0.3, 13,260.0?±?3.5, 6,153.0?±?1.6, and 58.0?±?3.8 mg/kg, respectively.  相似文献   
68.
Variations of micro- and macrominerals concentration in Swertia speciosa were determined by atomic absorption spectroscopy. The mineral elements showed significant changes in roots and leaves collected from different altitudes. Among all the elements, highest concentration (more than 2,000 mg/kg) of Ca and K were recorded in S. speciosa and the concentration of other elements analyzed in the study decreased in the order Fe>Na>Zn>Co>Li>Cu>Mn.  相似文献   
69.
Primary leaf explants of aseptically grown seedlings of moth bean [Vigna aconitifolia (Jacq.) Marechal] immersed in water or not were treated in microwave oven (2450 MHz, 800 W cm−2) for 1, 3, 5 and 7 s before culturing. Callusing and shoot emergence from these explants were enhanced up to microwave exposure lasted 5 s while longer treatment of water-immersed explants delayed callusing. One polypeptide (26.6 kD) was up regulated in the callus derived from microwave treatment in water-immersed explants. RAPD analysis detected alteration in DNA sequences due to microwave treatment in water-immersed explants for 7 s. The frequency of mutation was 1.6 % (4 bands out of 248) over all the cultures analyzed and the same was 13 % (4 bands out of 31), if amplicons generated at 7 s treatment alone were considered.  相似文献   
70.
Apurinic/apyrimidinic endonuclease (APE), an essential DNA repair enzyme, initiates the base excision repair pathway by creating a nick 5' to an abasic site in double-stranded DNA. Although the Chinese hamster ovary cells remain an important model for DNA repair studies, the Chinese hamster APE (chAPE1) has not been studied in vitro in respect to its kinetic characteristics. Here we report the results of a kinetic study performed on cloned and overexpressed enzyme in sf9 cells. The kinetic parameters were fully compatible with the broad range of kinetic parameters reported for the human enzyme. However, the activity measures depended on the time point of the culture. We applied inductivity coupled plasma spectrometry to measure the phosphorylation level of chAPE1. Our data showed that a higher phosphorylation of chAPE1 in the expression host was correlated to a lower endonuclease activity. The phosphorylation of a higher activity batch of chAPE1 by casein kinase II decreased the endonuclease activity, and the dephosphorylation of chAPE1 by lambda phosphatase increased the endonuclease activity. The exonuclease activity of chAPE1 was not observed in our kinetic analysis. The results suggest that noticeable divergence in reported activity levels for the human APE1 endonuclease might be caused by unaccounted phosphorylation. Our data also demonstrate that only selected kinases and phosphatases exert regulatory effects on chAPE1 endonuclease activity, suggesting further that this regulatory mechanism may function in vivo to turn on and off the function of this important enzyme in different organisms.  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