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   1096篇
  免费   111篇
  国内免费   24篇
  2023年   23篇
  2022年   35篇
  2021年   51篇
  2020年   49篇
  2019年   101篇
  2018年   44篇
  2017年   35篇
  2016年   45篇
  2015年   25篇
  2014年   49篇
  2013年   93篇
  2012年   39篇
  2011年   34篇
  2010年   24篇
  2009年   21篇
  2008年   28篇
  2007年   31篇
  2006年   29篇
  2005年   34篇
  2004年   23篇
  2003年   30篇
  2002年   19篇
  2001年   20篇
  2000年   15篇
  1999年   7篇
  1998年   15篇
  1997年   8篇
  1996年   22篇
  1995年   16篇
  1994年   21篇
  1993年   15篇
  1992年   11篇
  1991年   10篇
  1990年   17篇
  1989年   9篇
  1988年   19篇
  1987年   12篇
  1986年   20篇
  1985年   18篇
  1984年   24篇
  1983年   8篇
  1982年   24篇
  1981年   15篇
  1980年   8篇
  1979年   11篇
  1978年   4篇
  1976年   3篇
  1974年   4篇
  1973年   4篇
  1972年   3篇
排序方式: 共有1231条查询结果,搜索用时 15 毫秒
21.
Although the present experimental use of recombinant human granulocyte-colony-stimulating factor (rG-CSF) has been proven to alleviate the myelosuppression induced by antitumor chemotherapy, it is also believed to stimulate growth of some nonhematopoietic tumor cells. We investigated both the direct and indirect effects of rG-CSF on in vitro colony formation of human bladder cancer cell lines using a modified human tumor clonogenic assay. Peripheral blood mononuclear cells (PBMC) were used as feeder cells (a mixture of 5×104 monocytes/dish and 5×105 lymphocytes/dish obtained from healthy donors). Human bladder cancer cell lines KK-47, TCCSUP and T24, all derived from human transitional-cell carcinomas, were incubated continuously with various concentrations of rG-CSF ranging from 0.01 ng/ml to 10 ng/ml both with and without PBMC for 7–21 days. The concentrations of rG-CSF used were chosen as being in the range of achievable serum concentrations in patients treated with rG-CSF. At the end of incubation, colonies were counted under an inverted phase-contrast microscope, and an increase in the number of colonies in comparison with the control was used to evaluate the effects of rG-CSF. Results were expressed as a percentage of controls. rG-CSF in the upper layer at concentrations ranging from 0.1 ng/ml to 10 ng/ml stimulated the colony formation of all the cancer cell lines tested in the absence of PBMC in the feeder layer, whereas cells with PBMC in the feeder layer were significantly stimulated more than those without PBMC in the feeder layer (P<0.05) up to a certain concentration, which varied from cell line to cell line. At higher concentrations of rG-CSF, no further stimulation but, on the contrary, a decrease in colony formation was observed in cells with PBMC in the feeder layer in all the cell lines tested. Colony formation in KK-47 and T24 cell lines was significantly inhibited at 5 ng/ml and/or 10 ng/ml rG-CSF compared with cells without PBMC in the feeder layer. Our results suggest that rG-CSF may have both direct and indirect stimulatory effects on the growth of human bladder cancer cell lines in vitro. The results obtained also raise the possibility of adverse effects of rG-CSF in bladder cancer patients whose malignant cells may be directly and indirectly stimulated by this factor while it is being used clinically to alleviate the myelosuppression induced by antitumor chemotherapy.  相似文献   
22.
Enzymeimmunoassays (EIAs) for estrone conjugates (EC), pregnanediol-3-glucuronide (PDG), and C-19 and C-21 progesterone metabolites (C-19/C-21) were used to analyze urine samples from four nondomestic equid species, four tapir species, and two rhinoceros species in an attempt to identify if these assays could be used for diagnosing and monitoring pregnancy. The same urine samples were also analyzed for the presence of equine chorionic gonadotropin (eCG) activity, using a field dipstick test and a radioimmunoassay (RIA). The EC EIA was validated for three equid species and the Malayan tapir. Neither the PDG nor the C-19/C-21 EIAs were validated in any species evaluated. In equid species, the EC EIA demonstrated a specificity (the percentage of nonpregnant samples identified correctly) of 100% and a sensitivity (the percentage of pregnant samples identified correctly) of ≥ 88%. With the exception of the Grevy's zebra, the C-19/C-21 EIA showed a similar accuracy in identifying pregnant and nonpregnant equids. The PDG EIA was not sufficiently accurate to merit its use in equids or tapirs for pregnancy diagnosis. From the data collected, it appears analysis of a single urine by both the EC EIA and the C-19/C-21 EIA would be the best method of pregnancy detection during the last 2 trimesters of gestation, in equid species. In tapirs, the C-19/C-21 EIA was slightly more accurate for pregnancy diagnosis than the EC EIA. The C-19/C-21 EIA had a specificity of 93%, but a sensitivity of only 73% in tapir species. None of the EIAs evaluated demonstrated a sufficient specificity or sensitivity to be useful, as presently performed, for pregnancy diagnosis from a single sample in the black rhinoceros. The eCG dipstick used in this study did not prove a sufficiently reliable test for routine pregnancy in nondomestic equids. The eCG RIA results in the Przewalski's horses and the Hartman's mountain zebra were positive early in gestation, and indicate that gonadotropin analysis may be useful for pregnancy detection in these species. Only very low amounts of eCG activity was measured by the eCG RIA in the tapir and rhinoceros urine samples. © 1994 Wiley-Liss, Inc.  相似文献   
23.
Summary The spleen of the oriental fire-bellied toad, Bombina orientalis, consists of well-developed white pulp, separated from the lymphocytic marginal zone by the connective tissue boundary layer. Injection of peroxidase-conjugated rabbit anti-peroxidase revealed that these immune complexes were localized on the surface of acid-phosphatase-positive and non-specific-esterasepositive cells in the white pulp. The majority of immunecomplex-trapping cells were present around the blood vessels. Cell processes of some of these cells penetrated into the wall of blood vessels. The significance of the present findings is discussed with respect to the evolution of immune-complex-trapping cells in the spleen.  相似文献   
24.
25.
Phenelzine [2-phenylethylhydrazine] (PLZ), a potent inhibitor of monoamine oxidase (MAO)-A and-B, is used widely in psychiatry. We have studied the effects of PLZ administration on urinary excretion of several bioactive amines and their metabolites in psychiatric patients. Urine samples (24-hour) were collected prior to treatment and again at 2 and 4 weeks of treatment with PLZ (30–90 mg daily in divided doses). Amines and metabolites analyzed included 2-phenylethylamine (PEA), m-and p-tyramine (m-and p-TA), phenylacetic acid (PAA), m-and p-hydroxyphenylacetic acid (m-and p-OH-PAA), tryptamine (T), 5-hydroxytryptamine (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), normetanephrine (NME), 3-methoxy-4-hydroxyphenylglycol (MHPG), 3-methoxytyramine (3-MT), and homovanillic acid (HVA). Levels of PEA, p-TA, 5-HT, and T were elevated during treatment with PLZ, but no significant changes in urinary excretion of the acid metabolites PAA, p-OH-PAA, and 5-HIAA were observed. Urinary levels of the noradrenaline metabolites NME and MHPG were increased and decreased, respectively; a similar pattern was observed with the dopamine metabolites 3-MT and HVA. There was an elevation in levels of m-TA and a decrease in its acid metabolite m-OH-PAA during the treatment with PLZ.  相似文献   
26.
The accuracy of toad snapping towards moving worm dummies under various levels of dim illumination (from absolute threshold to moonlight) was videorecorded and related to spike responses of retinal ganglion cells exposed to equivalent stimuli. Some toads (at ca. 16 °C) successfully snapped at dummies that produced only one photoisomerization per 50 rods per second in the retina, in good agreement with thresholds of sensitive retinal ganglion cells. One factor underlying such high sensitivity is extensive temporal summation by the ganglion cells. This, however, is inevitably accompanied by very long response latencies (around 3 s near threshold), whereby the information reaching the brain shows the dummy in a position where it was several seconds earlier. Indeed, as the light was dimmed, snaps were displaced successively further to the rear of the dummy, finally missing it. The results in weak but clearly supra-threshold illumination indicate that snaps were aimed at the advancing head as seen by the brain, but landed further backwards in proportion to the retinal latency. Near absolute threshold, however, accuracy was too good, suggesting that the animal had recourse to a neural representation of the regularly moving dummies to correct for the slowness of vision.  相似文献   
27.
Dietary supplementation with a fish oil concentrate (FOC) reduced the endogenous synthesis of prostacyclin (PGI2), as measured by the excretion of its major urinary catabolite, 2,3-dinor-6-oxo-PGF (PGI2-M). Thirty-four healthy men (24–57 years old) were given controlled diets and supplements that provided 40% of the energy from fat and a minimum of 22 mg/d of α-tocopherol for two consecutive experimental periods of 10 weeks each. During the experimental periods, the men received capsules containing 15 g/d of a placebo oil (PO) (period 1) or 15 g/d of the FOC (period 2). In addition to the PO or FOC, capsules contained 1 mg of α-tocopherol per g of fat as an antioxidant. The average daily excretion of PGI2-M during the last week of FOC supplementation (period 2) was 22% less (P = 0.0001) than at the end of the first period. These results are at variance with those reported in comparable human studies conducted by other investigators during the middle and late 1980s. A 20% reduction (P = 0.003) in the 11-dehydrothromboxane B2 to 2,3-dinor-6-oxo-PGF excretion ratio at the end of period 2 in this study demonstrates that a shift of the n-6 to n-3 polyunsaturated fatty acid ratio from 12.5 to 2.3 brings about a substantial modulation of the eicosanoid system.  相似文献   
28.
摘要 目的:研究经会阴盆底超声联合血清雌二醇对女性压力性尿失禁(SUI)的诊断价值。方法:选取川北医学院附属医院2018年1月~2022年12月收治的女性SUI患者81例,记作观察组。另选取同期体检正常女性80例作为对照组。比较两组盆底超声参数以及血清雌二醇水平。采用受试者工作特征(ROC)曲线分析上述各项指标单独和联合检测的诊断效能。结果:观察组静息状态下近段尿道和人体纵轴间夹角(UIA)、最大Valsalva动作下近段尿道和膀胱后壁的夹角(PUVA)以及尿道旋转角(URA)相较于对照组较高(均P<0.05)。观察组血清雌二醇水平相较于对照组明显更低(P<0.05)。经ROC曲线分析发现:各项盆底超声参数联合血清雌二醇诊断女性SUI的效能优于各项指标单独诊断。结论:经会阴盆底超声可诊断女性SUI,在联合血清雌二醇时诊断女性SUI的价值更高。  相似文献   
29.
30.
The influence of application of skin-lightening creams and dental amalgam fillings on the urinary mercury (Hg) level was evaluated in 225 females (ages 17 to 58 years) living in Riyadh, capital of Saudi Arabia. The arithmetic mean of the urinary Hg level was 6.96 ± 20.43 g l, in the range 0 to 204.8 g l. The mean urinary Hg level adjusted by creatinine (Cr) was 11.22 ± 37.23 g g Cr, in the range 0 to 459.37 g g. No significant difference in urinary Hg was noted between the females regarding the use of skin-lightening creams. On the other hand, results showed that urinary Hg concentration was influenced by the use and number of dental amalgam fillings. No women were identified with symptoms or signs that could be attributed to Hg intoxication. Urine analyses for creatinine, urea, uric acid, phosphorus, magnesium, glucose and calcium showed significant correlation with urinary Hg. This suggests that chronic exposure to Hg may be associated with a deterioration of renal function.  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