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   4424篇
  免费   455篇
  国内免费   122篇
耳鼻咽喉   54篇
儿科学   58篇
妇产科学   94篇
基础医学   506篇
口腔科学   132篇
临床医学   502篇
内科学   432篇
皮肤病学   52篇
神经病学   173篇
特种医学   230篇
外科学   497篇
综合类   724篇
预防医学   378篇
眼科学   136篇
药学   609篇
  5篇
中国医学   250篇
肿瘤学   169篇
  2024年   8篇
  2023年   102篇
  2022年   152篇
  2021年   306篇
  2020年   265篇
  2019年   199篇
  2018年   192篇
  2017年   214篇
  2016年   184篇
  2015年   185篇
  2014年   350篇
  2013年   343篇
  2012年   259篇
  2011年   265篇
  2010年   185篇
  2009年   164篇
  2008年   170篇
  2007年   166篇
  2006年   147篇
  2005年   118篇
  2004年   82篇
  2003年   83篇
  2002年   82篇
  2001年   55篇
  2000年   67篇
  1999年   55篇
  1998年   51篇
  1997年   42篇
  1996年   49篇
  1995年   44篇
  1994年   41篇
  1993年   37篇
  1992年   37篇
  1991年   21篇
  1990年   25篇
  1989年   26篇
  1988年   25篇
  1987年   25篇
  1986年   27篇
  1985年   25篇
  1984年   22篇
  1983年   7篇
  1982年   19篇
  1981年   23篇
  1980年   11篇
  1979年   17篇
  1978年   7篇
  1977年   5篇
  1976年   5篇
  1973年   3篇
排序方式: 共有5001条查询结果,搜索用时 15 毫秒
1.
目的:运用新型光学生物测量仪IOL Master 700测量白内障超声乳化手术前后眼部生物学参数的变化,并探讨人工晶状体(IOL)屈光度数计算公式的选择。

方法:前瞻性研究。收集2021-01/06在苏州大学附属第一医院就诊的白内障患者52例57眼。术前和术后3mo使用IOL Master 700完成眼轴长度(AL)、前房深度(ACD)、角膜曲率(Km)的测量并分析。对不同IOL公式计算时预留的目标屈光值与术后3mo全自动验光仪实际屈光值结果进行比较并分析。

结果:手术前后测量的AL平均值分别为24.20±1.86、24.09±1.86mm,术后AL缩短了0.11mm; ACD值分别为3.08±0.44、4.55±0.36mm(P<0.001),术后ACD加深1.49mm; Km值分别为44.14±1.86、44.14±1.82D(P>0.05)。术前选用Barrett Universal Ⅱ公式所测结果的屈光误差最小,其次是Holladay Ⅱ及SRK/T公式,Holladay Ⅰ公式所测结果的误差最大(P<0.05)。

结论:白内障术后AL缩短以及ACD加深,度数测算时可考虑增加0.1mm的校正因子。IOL屈光度数计算公式中Barrett Universal Ⅱ公式预测性最佳,其次是Holladay Ⅱ及SRK/T公式。  相似文献   

2.
In this prospective study, we investigated the impact of SARS-CoV-2 infection on semen parameters in a cohort of men who had recently recovered from COVID-19. A total of 24 men who had recently recovered from mild COVID-19 were included in the study. Their semen parameters were normal before COVID-19 according to the World Health Organization 2010 reference values. Semen samples were collected from these participants in the recovery phases of COVID-19. To determine the effect of SARS-CoV-2 infection on semen parameters, the patients' pre-COVID-19 and post-COVID-19 semen analyses were compared. The mean age of the participants was 34.7 ± 6.4 years. The median interval between the positive nasopharyngeal swab test and obtaining semen samples was 111.5 (158) days. There was no significant difference in semen parameters before and after COVID-19 in terms of semen volume (p = .56), sperm concentration (p = .06), and progressive motility (p = .14). Total motility (p = .01) and total motile sperm count (p = .02) decreased significantly after SARS-CoV-2 infection compared to the pre-infection values. This study demonstrated that sperm motility and total motile sperm count were the semen parameters which showed a significant reduction in cases with a history of mild COVID-19.  相似文献   
3.
目的对近距离治疗计划的剂量参数在Oncentra治疗计划系统与MIM系统间产生的差异进行分析和研究。方法选取本院的43例妇科肿瘤患者近距离治疗计划,按照临床要求所有病例的靶区D90达到处方剂量。评估参数包括:靶区体积和D90,处方剂量总体积,靶区内的处方剂量体积以及危及器官包括:直肠,膀胱,小肠的D0.01cc,D1cc,D2cc。结果计划系统中的靶区体积和处方剂量值均明显小于MIM系统中相应的值(P<0.05),两系统显示出的处方体积相差不大。MIM系统中的靶区D90(676.74±54.82)cGy小于处方剂量,危及器官的受量则正好相反,即计划系统比MIM系统中相应的参数要小,其中直肠和膀胱的D0.01cc,D1cc,D2c,小肠的D0.01cc,D2cc的在两系统显示的值的差异均有统计学意义(P<0.05)。结论不同系统间传输相同的剂量和轮廓文件,DVH参数存在一定的差异,其主要原因是在不同系统对已勾画的各种器官轮廓计算体积存在算法上的不同。基于此,建议近距离计划在CT扫描时,尽量小的层厚可以消除或减少这种差异。  相似文献   
4.
5.
BackgroundPrevious studies on the age-, climate, and skin care habit-related changes of biophysical parameters have mainly focused on Caucasians, and studies on Asians are in paucity.ObjectiveThis study was aimed to investigate the variations of cutaneous biophysical parameters in Chinese and Korean women (northeast Asians) and to assess the association between those parameters and age, climate, and cosmetic habits.MethodsA cross-sectional study included 361 healthy Chinese and Korean women between 18 and 49 years of age in 4 cities (Guangzhou, Nanjing, and Shijiazhuang in China, and Suwon in Korea). We measured skin surface temperature, hydration, transepidermal water loss (TEWL), sebum, elasticity, skin pore, wrinkle, and skin tone (brightness) using non-invasive instruments. Demographic profiles and cosmetic habits were assessed using a questionnaire.ResultsSkin elasticity and tone decreased, and pore size and wrinkle increased with age. Subjects in Suwon (Korean) showed higher hydration level, lower TEWL and lower sebum, less severe wrinkle and brighter skin than those in the 3 cities in China. After adjusting for age and region, using sunscreen everyday, wearing base makeup daily, and using moisturizers improved hydration, TEWL, and elasticity significantly.ConclusionWomen in Suwon (Korea) were found to have a better profile of biophysical parameters than women in the 3 Chinese cities, which might be attributed to cosmetic habits, besides age and climatic factors. The fact that appropriate cosmetic habits are associated with favorable skin biophysical parameters underscores the importance of daily skin care routine in preserving skin functions.  相似文献   
6.
18F-脱氧葡萄糖(18F-FDG)PET/CT在恶性肿瘤的早期诊断、临床分期、疗效评价、监测复发及肿瘤放疗靶区定位中具有重要价值。为了使PET/CT能够更准确地进行恶性肿瘤的疗效评价,18F-FDG PET/CT代谢的可重复性研究显得尤为重要。本文就传统临床代谢参数值标准化摄取值(SUV)、代谢活性肿瘤体积(MATV)、总病灶糖酵解(TLG)、肿瘤与肝脏比率(TLR)、肿瘤与血液比率(SUR)及近年新兴的PET图像纹理分析等方面的可重复性研究进行概述。  相似文献   
7.
目的:探讨内镜活检胃癌组织中黏蛋白3A(MUC3A)、黏蛋白13(MUC13)表达及与病理参数和预后的关系。方法:选取2013年1月至2014年12月南阳市中心医院肿瘤科收治的接受内镜活检的116例患者胃癌组织和癌旁正常组织进行分析,采用免疫组织化学法检测所有组织样本中MUC3A,MUC13表达,观察二者表达情况,并分析二者与临床病理参数及预后的关系。结果:胃癌患者组织MUC3A,MUC13阳性率分别为68.97%和66.38%,高于正常组织的32.76%和7.76%(P<0.05);胃癌组织中MUC3A,MUC13表达与年龄、性别、肿瘤大小无关(P>0.05),与组织分化、浸润深度、TNM分期、淋巴结转移有关(P<0.05);随访5年结果显示:胃癌组织中MUC3A阳性患者中位生存时间为(40.50±1.95)个月,低于阴性患者的(48.67±2.51)个月(P<0.05),MUC3A阳性患者预后5年生存率为32.50%,低于阴性患者的55.56%(P<0.05);MUC13阳性患者中位生存时间为(38.52±1.92)个月,低于阴性患者的(49.06±2.71)个月(P<0.05),MUC13阳性患者预后5年生存率为30.00%,低于阴性患者的61.11%(P<0.05);COX多因素回归分析显示:TNM分期,淋巴结转移,MUC3A,MUC13是影响胃癌预后的独立危险因素(P<0.05)。结论:MUC3A,MUC13在胃癌组织中呈高表达,且与临床病理参数及预后密切相关,二者均有望作为判定胃癌发生发展及预后评估的参考指标。  相似文献   
8.
Kinetic investigations of the quaternization reactions of poly[2‐(dimethylamino)ethyl methacrylate] (PDMAEMA) with alkyl halides (1‐iodobutane, 1‐iodoheptane, and 1‐iododecane) are carried out at different temperatures. For this purpose, a PDMAEMA (Mn = 17.8 kDa, Ð = 1.35) synthesized via reversible addition fragmentation chain transfer polymerization is utilized. The progress of the quaternization reactions is followed by proton nuclear magnetic resonance. As expected, the rate of quaternization is higher with increasing temperature. The experimental data are used to determine the following kinetic parameters: order of the reaction, Arrhenius' pre‐exponential factor, and activation energy. To the best of knowledge, this is the first contribution that provides detailed kinetic data of the quaternization reactions on PDMAEMA.  相似文献   
9.
BackgroundSubjects with transfemoral amputation (TFA) show an asymmetric gait pattern associated with a decreased ability to recover mechanical energy and an increased metabolic cost of walking.Research questionThis study aimed to identify the spatio-temporal and kinematic gait variables correlated with mechanical energy values in subjects with TFA and to observe the ability of the identified parameters to discriminate between TFA and controls according to the type of prosthesis.MethodsThe gait of 40 subjects with TFA was evaluated with a motion 3-D optoelectronic system. Nine subjects wore a mechanical prosthesis (TFAm), seventeen a C-Leg prosthesis (TFAc), and fourteen a Genium prosthesis (TFAg). Spatio-temporal and pelvic kinematic parameters were measured. Energy recovery was measured relative to the whole-body center of mass (CoM) kinematics as the fraction of mechanical energy recovered during each walking step (R-step). Correlation tests and multiple linear regression analyses were used to evaluate the correlation and association between kinematic and energy variables, respectively. Receiver operating characteristics curves were plotted to assess the ability of the correlated parameter to distinguish subjects with TFA from controls, and optimal cutoff point values were calculated according to the type of prosthesis.ResultsAmong the spatio-temporal and kinematic parameters correlated to R-step, only pelvic obliquity of the prosthetic side was significantly associated with R-step. It showed an excellent ability to discriminate between TFA and controls. Furthermore, pelvic obliquity showed an excellent discriminative ability in identifying TFAm and TFAc and a good discriminative ability in identifying TFAg from controls.SignificancePelvic obliquity plays an important role in energy recovery during gait for subjects using prosthetics. This information might be exploited to monitor the adaptation of subjects with TFA to prosthetic devices, to lower the energetic cost of walking potentially, and to reduce the long-term risks of secondary physical complications in prosthetic users.  相似文献   
10.
渗漉法是将经过处理的药材粉末置于渗漉器中,不断加入溶剂,并收集渗漉液的一种中药常用提取方法,具有设备简单,操作容易,适用药材范围广,能有效提取热不稳定成分或组分等优点,但也存在溶剂消耗量大,提取耗时长,后续浓缩工艺能耗大等不足。该文主要综述了中药渗漉常见设备类型、工艺影响因素、参数优化方法以及过程监测方面的研究进展。分析文献后认为粉末粒度、溶剂组成、浸渍时间、渗漉流速、溶剂用量是渗漉工艺的重要影响因素。目前在渗漉工艺在线监测时采用近红外光谱技术较多,偏最小二乘法是常用的定量建模方法。笔者认为借鉴"质量源于设计"理念进行工艺控制,深入探究渗漉工艺机制并研发工艺控制方法是今后的发展趋势,所以应该深入探索过程建模技术,完善过程优化技术,研发过程监测技术。构建渗漉过程模型时可考虑借鉴柱色谱工艺的机制模型和经验模型。优化渗漉工艺参数时应考虑药材品质变化的影响,也需要研发更加简便易用的方法以监测渗漉过程状态和渗漉液关键性质。  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