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   133篇
  免费   20篇
  2022年   1篇
  2021年   2篇
  2018年   1篇
  2017年   4篇
  2015年   5篇
  2014年   3篇
  2013年   8篇
  2012年   6篇
  2011年   5篇
  2010年   5篇
  2009年   5篇
  2008年   2篇
  2007年   6篇
  2006年   7篇
  2005年   5篇
  2004年   5篇
  2003年   5篇
  2002年   7篇
  2001年   2篇
  2000年   3篇
  1999年   2篇
  1998年   3篇
  1997年   1篇
  1994年   2篇
  1993年   1篇
  1991年   7篇
  1990年   2篇
  1989年   4篇
  1988年   5篇
  1987年   3篇
  1986年   4篇
  1985年   5篇
  1984年   1篇
  1983年   4篇
  1982年   5篇
  1981年   1篇
  1980年   3篇
  1979年   2篇
  1975年   1篇
  1974年   1篇
  1973年   2篇
  1972年   1篇
  1971年   1篇
  1970年   2篇
  1969年   1篇
  1967年   2篇
排序方式: 共有153条查询结果,搜索用时 78 毫秒
1.
Because of the rise in incidence of upper urinary tract tumors, there is a need for a simple and reliable method for diagnosing these tumors, especially in people in a "high-risk" group. This retrospective study showed the usefulness of cytology and cytomorphometry in making the diagnosis of transitional-cell carcinoma of the upper urinary tract. The study also emphasized that the methods of collection and processing are of the utmost importance: the cytologic evaluation of ureteral catheterized urine specimens gave 100% accuracy as compared with a 40% false-negative rate in the cytologic diagnosis of voided urine specimens. A higher accuracy of urinary cytology for the diagnosis of upper urinary tract lesions clearly requires selective catheterization of the ureter. Objective cytomorphologic grading of the urinary cytology specimens was shown to compare favorably with histologic grading. Cytomorphologic grading not only can offer important information in determining the prognosis and in planning treatment but can also assist in quality control of other diagnostic methods and can help to resolve apparent diagnostic discrepancies.  相似文献   
2.
The development of a new population of Leydig cells after specific elimination of existing Leydig cells in mature rats by ethylene dimethanesulphonate (EDS) was characterized by investigating the testicular activities of 5 alpha-reductase and non-specific esterase, the serum concentrations of 3 alpha-androstanediol and testosterone and the Leydig cell morphology. Plasma concentrations of both androgens were strongly reduced up to 15 days after administration of EDS. Thereafter, in contrast to the gradual and continuous increase of serum testosterone values, the changes in serum 3 alpha-androstanediol were transient, with the highest level on Day 35. The temporal pattern of testicular 5 alpha-reductase activity was almost similar to that of serum 3 alpha-androstanediol. The testicular esterase activity increased gradually from Day 25 until Day 76. The temporal changes in steroid concentrations and enzyme activities after EDS administration indicate that the development of the Leydig cells in EDS-treated rats occurs in a fashion similar to that in pubertal rats. However, the numerous lipid droplets and large nuclei in these Leydig cells indicate that these cells may also be classified as fetal cells. It is concluded that, after treatment with EDS, fetal and pubertal characteristics are present in Leydig cells. It is, however, unknown whether both characteristics are present in one or in two distinct cell populations.  相似文献   
3.
4.
The invasively growing and metasizing Lewis lung carcinoma consistently contained urokinase-type plasminogen activator (u-PA) enzyme activity. When investigated immunocytochemically with antibodies against u-PA, different parts of individual tumors showed a pronounced heterogeneity in staining intensity. Strong staining was found in areas with invasive growth and degradation of surrounding normal tissue, while other areas were completely devoid of staining. Immunoreactivity occurred both with a perinuclear cytoplasmic localization in tumor cells and associated with apparently extracellular material. SDS PAGE of tumor extracts, under both reducing and nonreducing conditions, followed by immunoblotting, showed only one immunocytochemically stainable band with an electrophoretic mobility corresponding to that of purified proenzyme to u-PA, while no two-chain u-PA was detected. This indicates that the major part of the activator in Lewis lung carcinoma is present as one-chain pro-u-PA.  相似文献   
5.
The flash-induced absorbance change measured at 518 nm (P515) in intact chloroplasts consists of at least 4 kinetically different components. Here the non-electrochromic component, either called phase d or reaction 3, is studied in some detail. The effect of DCMU, DQH2 and DBMIB on the amplitude of reaction 3 and the turnover of cytochrome f and P700 have been monitored, suggesting an involvement of photosystem 1 in the activation of the non-electrochromic absorbance change. This is confirmed by the parallel oscillation pattern found in P700 rereduction and the amplitude of reaction 3.  相似文献   
6.
A gene encoding a protein homologous to the periplasmic ABC phosphate binding receptor PstS from Escherichia coli was cloned and sequenced from a lambda gt11 library of Mycobacterium tuberculosis by screening with monoclonal antibody 2A1-2. Its degree of similarity to the E. coli PstS is comparable to those of the previously described M. tuberculosis phosphate binding protein pab (Ag78, Ag5, or 38-kDa protein) and another M. tuberculosis protein which we identified recently. We suggest that the three M. tuberculosis proteins share a similar function and could be named PstS-1, PstS-2, and PstS-3, respectively. Molecular modeling of their three-dimensional structures using the structure of the E. coli PstS as a template and their inducibility by phosphate starvation support this view. Recombinant PstS-2 and PstS-3 were produced and purified by affinity chromatography. With PstS-1, these proteins were used to demonstrate the specificity of three groups of monoclonal antibodies. Using these antibodies in flow cytometry and immunoblotting analyses, we demonstrate that the three genes are expressed and their protein products are present and accessible at the mycobacterial surface as well as in its culture filtrate. Together with the M. tuberculosis genes encoding homologs of the PstA, PstB, and PstC components we cloned before, the present data suggest that at least one, and possibly several, related and functional ABC phosphate transporters exist in mycobacteria. It is hypothesized that the mycobacterial gene duplications presented here may be a subtle adaptation of intracellular pathogens to phosphate starvation in their alternating growth environments.  相似文献   
7.
The clinical value and limitations of a previously described cytomorphometric method, based on nuclear size and anisonucleosis, for evaluation of routine fine-needle aspiration of the breast were assessed in a series of 313 histologically investigated primary breast lesions. Limitations were analyzed by histomorphometry and DNA flow cytometry in 116 consecutive cases of histologically confirmed breast carcinoma. Eighty per cent of histologically proven malignant tumours were classified cytomorphometrically as malignant and no false-positive results were encountered. For benign lesions a benign cytomorphometric classification was reached in 66% of the cases. Histomorphometry showed that on the whole the assignment of histologically malignant tumours to a non-malignant cytomorphometric classification was determined by smaller nuclei and not by sampling error. Tumours assigned to a malignant cytomorphometric classification had on average significantly higher DNA indices than did tumours not assigned to a malignant cytomorphometric classification (P less than 0.001). The mean-nuclear areas in cytomorphometry and histomorphometry were strongly correlated with DNA indices indicated by DNA flow cytometry (P less than 0.001 for both). The present findings show that this cytomorphometric method is appropriate for routine quality control of a cytological diagnosis of malignancy in FNA of the breast. However, an inconclusive result in 15-25% of the tumours is inevitable.  相似文献   
8.
Abstract

Post-construction avifauna investigations were undertaken at Project West Wind, Meridian Energy Limited's 62-turbine wind farm on the Wellington south coast. These investigations were required in accordance with the resource consent conditions to quantify the level of avian mortalities occurring at the wind farm, particularly in regard to New Zealand falcon (Falco novaeseelandiae), kākā (Nestor meridionalis) and kererū (Hemiphaga novaeseelandiae). This is the first comprehensive study at a New Zealand operating wind farm. The methods included three field components necessary to calculate annual estimates of mortalities across the wind farm site: routine turbine searches; carcass detection trials; and carcass removal trials. Results from years 1 and 2 of a three-year programme are presented. To date, mortalities have been recorded for 17 taxa at 18 of the 24 study turbines. There have been no recorded mortalities of falcon, kākā or kererū. Australasian harrier (Circus approximans) has been the species for which the most mortalities have been recorded. Overall estimated annual mortality rates for years 1 and 2 were calculated to be approximately six and five birds per turbine respectively.  相似文献   
9.
Feline leukemia virus (FeLV) is a naturally transmitted gammaretrovirus that infects domestic cats. FeLV-945, the predominant isolate associated with non-T-cell disease in a natural cohort, is a member of FeLV subgroup A but differs in sequence from the FeLV-A prototype, FeLV-A/61E, in the surface glycoprotein (SU) and long terminal repeat (LTR). Substitution of the FeLV-945 LTR into FeLV-A/61E resulted in pathogenesis indistinguishable from that of FeLV-A/61E, namely, thymic lymphoma of T-cell origin. In contrast, substitution of both FeLV-945 LTR and SU into FeLV-A/61E resulted in multicentric lymphoma of non-T-cell origin. These results implicated the FeLV-945 SU as a determinant of pathogenic spectrum. The present study was undertaken to test the hypothesis that FeLV-945 SU can act in the absence of other unique sequence elements of FeLV-945 to determine the disease spectrum. Substitution of FeLV-A/61E SU with that of FeLV-945 altered the clinical presentation and resulted in tumors that demonstrated expression of CD45R in the presence or absence of CD3. Despite the evident expression of CD45R, a typical B-cell marker, T-cell receptor beta (TCRβ) gene rearrangement indicated a T-cell origin. Tumor cells were detectable in bone marrow and blood at earlier times during the disease process, and the predominant SU genes from proviruses integrated in tumor DNA carried markers of genetic recombination. The findings demonstrate that FeLV-945 SU alters pathogenesis, although incompletely, in the absence of FeLV-945 LTR. Evidence demonstrates that FeLV-945 SU and LTR are required together to fully recapitulate the distinctive non-T-cell disease outcome seen in the natural cohort.  相似文献   
10.
APOBEC3G (A3G) is a cytidine deaminase that restricts human immunodeficiency virus type 1 (HIV-1) and other lentiviruses. Most of these viruses encode a Vif protein that directly binds A3G and leads to its proteasomal degradation. Both Vif proteins of HIV-1 and African green monkey simian immunodeficiency virus (SIVagm) bind residue 128 of A3G. However, this position does not control the A3G degradation by Vif variants derived from HIV-2 and SIVmac, which both originated from SIV of sooty mangabey monkeys (SIVsmm), suggesting that the A3G binding site for Vif proteins of the SIVsmm/HIV-2 lineage differs from that of HIV-1. To map the SIVsmm Vif binding site of A3G, we performed immunoprecipitations of individual A3G domains, Vif/A3G degradation assays and a detailed mutational analysis of human A3G. We show that A3G residue 129, but not the adjacent position 128, confers susceptibility to degradation by SIVsmm Vif. An artificial A3G mutant, the P129D mutant, was resistant to degradation by diverse Vifs from HIV-1, HIV-2, SIVagm, and chimpanzee SIV (SIVcpz), suggesting a conserved lentiviral Vif binding site. Gorilla A3G naturally contains a glutamine (Q) at position 129, which makes its A3G resistant to Vifs from diverse lineages. We speculate that gorilla A3G serves as a barrier against SIVcpz strains. In summary, we show that Vif proteins from distinct lineages bind to the same A3G loop, which includes positions 128 and 129. The multiple adaptations within this loop among diverse primates underscore the importance of counteracting A3G in lentiviral evolution.  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