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   8240篇
  免费   468篇
  国内免费   193篇
  2023年   95篇
  2022年   134篇
  2021年   188篇
  2020年   152篇
  2019年   175篇
  2018年   161篇
  2017年   118篇
  2016年   150篇
  2015年   205篇
  2014年   306篇
  2013年   484篇
  2012年   263篇
  2011年   341篇
  2010年   242篇
  2009年   310篇
  2008年   342篇
  2007年   350篇
  2006年   322篇
  2005年   351篇
  2004年   301篇
  2003年   262篇
  2002年   263篇
  2001年   163篇
  2000年   123篇
  1999年   152篇
  1998年   142篇
  1997年   131篇
  1996年   134篇
  1995年   183篇
  1994年   139篇
  1993年   136篇
  1992年   122篇
  1991年   126篇
  1990年   106篇
  1989年   100篇
  1988年   129篇
  1987年   124篇
  1986年   82篇
  1985年   173篇
  1984年   159篇
  1983年   132篇
  1982年   159篇
  1981年   128篇
  1980年   99篇
  1979年   111篇
  1978年   77篇
  1977年   57篇
  1976年   53篇
  1974年   28篇
  1973年   43篇
排序方式: 共有8901条查询结果,搜索用时 15 毫秒
1.
目的:探讨胰岛素样生长因子-1(IGF-1)、转化生长因子-beta1(TGF-beta1)水平变化在过敏性紫癜患儿肾损害发病机制中作用。 方法:选取HSP患儿30 例、HSPN患儿30 例和30 例健康儿童为对照组,分别采血,用化学发光法检测各组标本IGF-1 浓度,采用 双抗体一步夹心法酶联免疫吸附试验检测各组TGF-茁1 浓度;同时用全自动生化仪检测各组患儿血清Cys C、BUN、SCr 水平。结 果:血IGF-1、TGF-beta1 的水平HSPN组、HSP组与对照组患儿比较,差异均有统计学意义(P<0.05)。血清Cys C 水平对照组、HSP 组与HSPN 组患儿比较,差异有统计学意义(P<0.05)。采用直线相关分析HSPN 组的血清Cys C 水平与血IGF-1、TGF-beta1 水平 比较,存在正相关(r=0.759、r=0.802,均P<0.05),血IGF-1 与TGF-beta1 也存在正相关(r=0.850,P<0.05)。结论:血IGF-1、TGF-beta1 共同 参与紫癜性肾炎发病,其水平变化与病理损害程度相关。  相似文献   
2.
目的:探究雌激素联合丹栀逍遥胶囊对更年期综合征妇女生殖内分泌系统及免疫功能的调节作用。方法:选取2014年5月至2014年9月我院收治的女性更年期综合症患者60例并将其随机分为两组,其中对照组给予雌激素替代等临床常规疗法;实验组在雌激素替代治疗基础上加用丹栀逍遥胶囊联合治疗。观察并比较两组患者生殖内分泌激素(E2、FSH、LH)水平、T淋巴细胞亚群(CD3+、CD4+、CD8+、CD4+/CD8+)比例以及IL-2活性的变化。结果:治疗后,两组血清E2、CD3+、CD4+、CD4+/CD8+水平及IL-2活性均较治疗前显著升高,而FSH、LH水平均明显低于治疗前,且实验组治疗后E2、CD3+、CD4+、CD4+/CD8+水平及IL-2活性显著高于对照组,FSH、LH水平均明显低于对照组,差异均有统计学意义(P0.05)。结论:雌激素联合丹栀逍遥胶囊能更加有效调节女性更年期综合征患者生殖内分泌激素水平,提高免疫功能,值得临床推广。  相似文献   
3.
目的:探讨STZ诱导糖尿病大鼠ghrelin和nesfatin-1动力学及分泌调节变化。方法:STZ诱导糖尿病大鼠模型;采用葡糖糖脱氢酶分析法测量血浆葡萄糖水平;免疫放射分析检测血浆ghrelin、nesfatin-1、胰岛素、胰岛素样生长因子1(IGF-1)、生长激素(GH)含量;采用real-time PCR检测ghrelin m RNA水平变化;免疫组化观察ghrelin和nesfatin-1免疫活性细胞数量。结果:糖尿病大鼠体重显著降低(t=23.16,P<0.01),血糖水平显著升高(t=22.55,P<0.01),血浆胰岛素和IGF-1水平显著降低(t=6.50,t=24.13,P<0.01),但GH水平显著升高(t=3.30,P<0.05)。糖尿病大鼠血浆总ghrelin(t=7.03,P<0.01)和活性ghrelin(t=3.33,P<0.05)水平均显著升高,血浆nesfatin-1水平则显著降低(t=6.24,P<0.01);糖尿病大鼠血浆总ghrelin与GH(r=0.81,P<0.01)和IGF-1水平(r=-0.58,P<0.01)呈显著相关性;与对照组大鼠相比,糖尿病大鼠胃总ghrelin(t=16.86,P<0.01)和活性ghrelin(t=3.30,P<0.05)水平均显著降低;而胃nesfatin-1(t=7.93,P<0.01)水平则显著升高。胃总ghrelin水平与血浆IGF-1水平呈明显相关性(r=0.65,P<0.01);与对照组大鼠相比,糖尿病大鼠胃ghrelin m RNA表达水平显著升高(t=16.8,P<0.01),胃底ghrelin免疫活性细胞数量显著减少(t=3.98,P<0.01);实验中给予大鼠自由饮食,糖尿病大鼠血浆总ghrelin水平显著增加(t=7.53,P<0.01),nesfatin-1水平显著降低(t=5.46,P<0.01)。糖尿病大鼠注射胰岛素后,可使增加的ghrelin水平(t=1.76,P=0.11)和降低的nesfatin-1水平接近正常(t=1.96,P=0.06);且胰岛素可显著反转糖尿病大鼠胃总ghrelin(t=8.54,P<0.01)和nesfatin-1水平(t=2.42,P<0.05);以及注射胰岛素后,糖尿病大鼠胃底ghrelin细胞显著增加,nesfatin-1细胞明显减少(t=3.21,t=2.59,P<0.05)。结论:Ghrelin或nesfatin-1参与糖尿病大鼠能量平衡调控。  相似文献   
4.
5.
目的:对腹腔镜下行卵巢囊肿剥除术患者在手术前和手术后的AMH(anti-mullerian hormone,抗苗勒氏管激素)和bFSH(basic Follicle-stimulating hormone,基础促卵泡刺激素)含量进行测定,分析其临床意义和价值。方法:将2012年1月~2014年1月期间来我院妇产科就诊的34例卵巢巧克力囊肿患者作为研究组,上述患者经相关检查均身体状况符合腹腔镜手术的要求,并选取同期36例非巧囊患者作为对照组,2组患者均实施腹腔镜下卵巢囊肿剥离术进行治疗,并分别在手术前和手术完毕时对患者的AMH和bFSH水平进行测定。结果:研究组与对照组患者在手术完毕后AMH含量[(2.02±2.11,2.77±1.62)ng/m L]同手术前[(2.88±2.30,3.08±1.81)ng/m L]对比具有明显降低,具有统计学差异,(P0.05),研究组患者降低水平更为显著;研究组手术完毕b FSH含量(6.83±1.80)μU/m L明显高于术前(6.29±2.11)μU/m L,具有统计学差异(P0.05),而对照组患者术后血清bFSH含量同术前比较并未明显上升,无统计学差异(P0.05)。结论:行腹腔镜卵巢囊肿剥除术能够使患者的卵巢储备能力下降,测定AMH较b FSH能够更好的反应出卵巢手术后卵巢储备状况。  相似文献   
6.
The effects of a high-growth genetic background on the growth of mice hemizygous for one of two growth hormone transgenes were examined. Male mice hemizygous for wild-type (W) and dwarf mutant (M) bovine growth hormone (bGH) transgenes were crossed with females of a high-growth selected (S) and control (C) line as follows: W x S, W x C, M x S and M x C. Body weights of progeny were recorded weekly from 2 to 10 weeks of age. F1 progeny were classified as carriers (P) or non-carriers (N) of the transgene by assaying tail DNA for bGH using the polymerase chain reaction and agarose gel electrophoresis. A deficiency in the number of f1 progeny carrying the W (P<0.05) and M (P<0.01) bGH transgene was most likely due to differential prenatal and early postnatal mortality. Bodyweight means of wild-type transgenic mice were larger (P < 0.05) than those of non-transgenic littermates by 3 weeks of age in a C background in contrast to 5 weeks in S. The wild-type bGH transgene increased adult body weights more in the C (155%) than in the S (136%) background, indicating transgene expression by selection background interaction (P < 0.05). However, the growth response to the wild-type transgene in the S background was still large. The dwarf mutant transgene had a greater effect on growth reduction in the S (70%) than in the C (84%) background, thus causing transgene expression by selection background interaction (P < 0.05). Gender by wild-type transgene effect interactions (P < 0.001) for adult body weight were caused by the transgene reducing the gender difference for body weight in C and eliminating it in S. The dwarf mutant caused a larger negative effect on growth in males than in females, resulting in a gender by dwarf mutant transgene interaction (P < 0.001) for adult body weights. Results indicate that the effect of a GH transgene on growth can be affected both by a high-growth genetic background and the gender of progeny.  相似文献   
7.
Abstract A cluster of five to seven AKH-like immunoreactive cells lie in each lobe of the paired corpora cardiaca of the true armyworm, Pseudaletia unipuncta. These cells form a mesh work of immunoreactive processes within the corpora cardiaca, and immunoreactive tracts projecting posteriorly over the aorta.
Reversed-phase high performance liquid chromatography of extracts of the corpora cardiaca of P.unipuncta revealed a single large U.V. absorbent peak with a retention time identical to synthetic Manduca- AKH. Amino acid analysis of the contents of this peak yielded a composition identical to that of synthetic Manduca-AKH which was analysed in a parallel manner. Furthermore the material within the peak possessed adipokinetic activity when bioassayed in day 2 adult male P. unipuncta. The corpora cardiaca of similar individuals were found to contain approximately 17.6ng (17.6pmol) of Manduca-AKH equivalents per pair.
Injection of Manduca-AKH into 2-day-old adult male P.unipuncta resulted in a dose-dependent elevation in haemolymph lipid levels with a maximum level of 80–90μmg/μl obtained with 5–10 ng of Manduca-AKH. Continuous flight also elevated haemolymph lipid levels in day 4 adult males with a significant elevation evident in the first samples taken after 15 min of flight and lipid levels plateauing at approximately 100 μg/μl by about 60 min of flight.  相似文献   
8.

Objective

Parotid gland incidentalomas are unexpected hypermetabolic foci in the parotid region that can be found when scanning the whole-body by PET/CT. The role of SUVmax is controversial to differentiate benign or malignant tumours in this indication. The aim of this study was to determine PET/CT features of malignant parotid incidentaloma, in order to improve medical care.

Methods

We retrospectively reviewed 10,756 PET/CT scans performed during 3?years at our center in search of parotid gland incidentalomas. Twenty-eight patients were included. For each lesion, we have collected the results of parotid MRI, histology and/or subsequent imaging. Logistic regression was used to compare SUVmax, SUVmean, MTV and TLG, and ROC curves were used to assess threshold values.

Results

Prevalence of parotid gland incidentalomas was 1.29% (n?=?139). Thirty-seven were included, among them, 46% were malignant. SUVmax, MTV and TLG were significantly higher for malignant tumours (P?≤?0.001). MTV?>?4?mL and TLG?>?7.5?mL were strongly associated with a malignant lesion (MTV and TLG: P?<?0.001; SUVmax: P?=?0.005; SUVmean: P?=?0.07). According to ROC curves, MTV thresholded at 4 had an AUC of 0.92 (Se 75%, Sp 100%) to differentiate benign and malignant lesions.

Conclusions

MTV and TLG were predictive factors of malignancy, stronger than SUVmax. However, given the high proportion of malignant lesions and the suboptimal sensitivity of the MTV further exploration must be requested for any parotid gland incidentaloma.  相似文献   
9.
Peptidomimetics are designed to overcome the poor pharmacokinetics and pharmacodynamics associated with the native peptide or protein on which they are based. The design of peptidomimetics starts from developing structure-activity relationships of the native ligand-target pair that identify the key residues that are responsible for the biological effect of the native peptide or protein. Then minimization of the structure and introduction of constraints are applied to create the core active site that can interact with the target with high affinity and selectivity. Developing peptidomimetics is not trivial and often challenging, particularly when peptides’ interaction mechanism with their target is complex. This review will discuss the challenges of developing peptidomimetics of therapeutically important insulin superfamily peptides, particularly those which have two chains (A and B) and three disulfide bonds and whose receptors are known, namely insulin, H2 relaxin, H3 relaxin, INSL3 and INSL5.  相似文献   
10.
《Current biology : CB》2020,30(2):298-303.e3
  1. Download : Download high-res image (251KB)
  2. Download : Download full-size image
  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