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   2993篇
  免费   150篇
  国内免费   16篇
耳鼻咽喉   32篇
儿科学   55篇
妇产科学   27篇
基础医学   395篇
口腔科学   45篇
临床医学   196篇
内科学   1058篇
皮肤病学   23篇
神经病学   227篇
特种医学   58篇
外科学   438篇
综合类   7篇
预防医学   83篇
眼科学   44篇
药学   187篇
中国医学   9篇
肿瘤学   275篇
  2023年   21篇
  2022年   28篇
  2021年   68篇
  2020年   37篇
  2019年   56篇
  2018年   77篇
  2017年   37篇
  2016年   61篇
  2015年   48篇
  2014年   78篇
  2013年   88篇
  2012年   152篇
  2011年   201篇
  2010年   89篇
  2009年   94篇
  2008年   148篇
  2007年   177篇
  2006年   214篇
  2005年   179篇
  2004年   196篇
  2003年   180篇
  2002年   147篇
  2001年   49篇
  2000年   58篇
  1999年   46篇
  1998年   54篇
  1997年   31篇
  1996年   28篇
  1995年   22篇
  1994年   24篇
  1993年   25篇
  1992年   40篇
  1991年   41篇
  1990年   41篇
  1989年   28篇
  1988年   27篇
  1987年   23篇
  1986年   24篇
  1985年   27篇
  1984年   15篇
  1983年   25篇
  1982年   10篇
  1981年   12篇
  1980年   11篇
  1979年   16篇
  1978年   11篇
  1977年   11篇
  1972年   10篇
  1969年   12篇
  1967年   12篇
排序方式: 共有3159条查询结果,搜索用时 15 毫秒
1.
A Bochdalek hernia (BH) is a congenital abnormality with incomplete closure of the diaphragm. It is usually manifested in infants but rarely in adults. Here, we report an adult patient with gastric volvulus and giant BH that were safely repaired by endoscopic reduction and elective laparoscopic surgery, respectively. A 79-year-old woman presented with left upper abdominal pain but no history of trauma. CT revealed a giant BH with gastric volvulus. After emergency endoscopic reduction of the volvulus, elective laparoscopic repair of the BH was performed. The 8 × 8-cm defect was repaired with interrupted nonabsorbable sutures and a mesh. The patient's postoperative course was uneventful, and no complications or recurrence were observed in the 6 months that followed.  相似文献   
2.
A 1:1 adduct of methyl sorbate (MS) and 1,3‐di‐tert‐butylimidazol‐2‐ylidene (NHCtBu) initiates anionic polymerization of a nonconjugated polar alkene, allyl methacrylate (AMA) in toluene at ?20 °C. After the monomer is consumed quantitatively using a bulky aluminum Lewis acid, methylaluminum bis(2,6‐di‐tert‐butyl‐4‐methylphenoxide) (MAD), as an additive, successive ring‐closure occurs without highly dilute conditions to give a cyclic poly(AMA) containing α‐terminal MS unit, and an Mn of 8.8 × 103?58.5 × 103 with a narrow molecular dispersity index (Mw/Mn = 1.14–1.37). The lack of a need for dilution is due to the fact that an α‐terminal NHCtBu group is acting as the counter cation for the propagating center in the polymerization. From 1H NMR and matrix assisted laser desorption/ionization (MALDI‐TOF) mass spectra, combined with transmittance electron microscope (TEM) observation of a synthesized poly(AMA) with longer alkyl side chains prepared via a thiol‐ene click reaction, it is concluded that once the monomer is consumed, nucleophilic attack at the neighboring methine of the α‐terminal NHCtBu residue by the propagating anionic center causes ring‐closing to cyclic poly(AMA).  相似文献   
3.
OBJECTIVE: The Karolinska sleepiness scale (KSS) is frequently used for evaluating subjective sleepiness. The main aim of the present study was to investigate the validity and reliability of the KSS with electroencephalographic, behavioral and other subjective indicators of sleepiness. METHODS: Participants were 16 healthy females aged 33-43 (38.1+/-2.68) years. The experiment involved 8 measurement sessions per day for 3 consecutive days. Each session contained the psychomotor vigilance task (PVT), the Karolinska drowsiness test (KDT-EEG alpha & theta power), the alpha attenuation test (AAT-alpha power ratio open/closed eyes) and the KSS. RESULTS: Median reaction time, number of lapses, alpha and theta power density and the alpha attenuation coefficients (AAC) showed highly significant increase with increasing KSS. The same variables were also significantly correlated with KSS, with a mean value for lapses (r=0.56). CONCLUSIONS: The KSS was closely related to EEG and behavioral variables, indicating a high validity in measuring sleepiness. SIGNIFICANCE: KSS ratings may be a useful proxy for EEG or behavioral indicators of sleepiness.  相似文献   
4.
To elucidate the growth of the tarsal bones in congenital clubfoot, relative to the growth of these bones in the unaffected feet and compared to growth in the feet of normal volunteers, we used a computed tomography (CT) scanner to measure the volume of all tarsal bones. The subjects of the study were 10 adults (7 men and 3 women) with unilateral congenital clubfoot (average age 20 years and 1 month). As controls, we examined 11 healthy volunteers. We calculated the ratio of the volume of each tarsal bone to the total bone volume and the ratio of the volume of each tarsal bone in clubfoot to the corresponding bone in the unaffected foot. The volume ratio of each tarsal bone was compared between clubfeet and unaffected feet because the differences of each tarsal bone ratio between the normal foot group and unaffected foot group were not significant. In the clubfeet (n=10), the talus and the medial cuneiform bones were smaller than those in the unaffected feet (n=10) but the cuboid bone was larger. The growth of the navicular did not differ from as that in unaffected feet. Our results suggested hypoplasia on the medial side of the foot in adult patients with congenital clubfoot. The 3 patients who had undergone medial release showed particularly marked hypoplasia of the medial side. In congenital clubfoot cases with severe deformities who had undergone wide soft-tissue release operations, there were clear growth suppressions in the talus and the medial cuneiform. We could not determine whether the cause of the growth suppression was the hypoplastic nature of tarsal bones themselves or the surgical obstacles to tarsal bone growth.  相似文献   
5.
The matrix metalloproteinase matrilysin (MMP-7) is a member of the matrix metallo-proteinase gene family, which is believed to play an important role in tumor invasion and metastasis. We have previously found that matrilysin mRNA is specifically expressed in colorectal cancers and adenomas and that its message is localized in the tumor cells themselves. We examined the effects of activated Ki-ras oncogene on the expression of matrilysin in colon cancer cells. We showed that both mRNA and the enzymatic activity of matrilysin were induced by the introduction of activated Ki-ras into SW1417 colon cancer cells. To understand the mechanisms regulating this induction, we analyzed alterations of AP-1 activity induced by activated Ki-ras, using the chloramphenicol acetyltransferase assay. AP-1 activity in SW1417 cells expressing activated Ki-ras was higher than that in control cells. The gel-shift assay also showed higher levels of AP-1 binding protein in SW1417 cells expressing activated Ki-ras than those in control cells. Our results suggest that activated Ki-ras may play a role in inducing expression of matrilysin through an AP-1-dependent pathway in colon cancer cells.  相似文献   
6.
A patient with a recurrent tumor in the trachea adjacent to the right main bronchus was treated by surgical resection 19 months after undergoing surgery for the primary cancer. The patient had previously undergone right upper lobectomy for T1N0M0 stage I squamous cell carcinoma. A carinal resection was performed which included 4 rings of the trachea, 2 rings of the righ main bronchus, and 1 ring of the left main bronchus. Reconstruction consisted of an end-to-end anastomosis of the trachea and left main bronchus, and an end-to-side anastomosis of the right and left main bronchi. The postoperative course was uneventful, and at present the patient is healthy 12 months following reoperation.  相似文献   
7.
Dopa-decarboxylase activity was high at 2-3 weeks of age, low at 5-6 weeks, and very low in adult rats; protease activity increased with age. Trypsin-like proteases, which decrease dopa-decarboxylase activity, were detected in the gland and were inhibited by a protease inhibitor, leupeptin. High concentrations (20 mg/ml) of leupeptin increased dopa-decarboxylase activity in the glands of adult rats to the level found at 5-6 weeks of age. The low activity of dopa decarboxylase in adult gland may be due in part to endogenous proteases.  相似文献   
8.
Background: A lung-protecting strategy is essential when ventilating acute lung injury/acute respiratory distress syndrome patients. Current emphasis is on limiting inspiratory pressure and volume. This study was designed to investigate the effect of peak inspiratory flow on lung injury.

Methods: Twenty-four rabbits were anesthetized, tracheostomized, ventilated with a Siemens Servo 300, and randomly assigned to three groups as follows: 1) the pressure regulated volume control group received pressure-regulated volume control mode with inspiratory time set at 20% of total cycle time, 2) the volume control with 20% inspiratory time group received volume-control mode with inspiratory time of 20% of total cycle time, and 3) the volume control with 50% inspiratory time group received volume-control mode with inspiratory time of 50% of total cycle time. Tidal volume was 30 ml/kg, respiratory rate was 20 breaths/min, and positive end-expiratory pressure was 0 cm H2O. After 6 h mechanical ventilation, the lungs were removed for histologic examination.

Results: When mechanical ventilation started, peak inspiratory flow was 28.8 +/- 1.4 l/min in the pressure regulated volume control group, 7.5 +/- 0.5 l/min in the volume control with 20% inspiratory time group, and 2.6 +/- 0.3 l/min in the volume control with 50% inspiratory time group. Plateau pressure did not differ significantly among the groups. Gradually during 6 h, Pao2 in the pressure regulated volume control group decreased from 688 +/- 39 to a significantly lower 304 +/- 199 mm Hg (P < 0.05) (mean +/- SD). The static compliance of the respiratory system for the pressure regulated volume control group also ended significantly lower after 6 h (P < 0.05). Wet to dry ratio for the pressure regulated volume control group was larger than for other groups (P < 0.05). Macroscopically and histologically, the lungs of the pressure regulated volume control group showed more injury than the other groups.  相似文献   

9.
To investigate the relationship between the effects of bone turnover and bone marrow cell development in bone cells, we developed a mouse voluntary climbing exercise model. Climbing exercise increased bone volume and transient osteogenic potential of bone marrow. This model would be suitable for investigating the mechanistic roles of mechanical loading. INTRODUCTION: The relationship between bone mass gain and local bone formation and resorption in mechanically loaded bone is not well understood. MATERIALS AND METHODS: Sixty-five C57BL/6J mice, 8 weeks of age, were assigned to five groups: a baseline control and two groups each of ground control and climbing exercise mice for 2 and 4 weeks. Mice were housed in a 100-cm tower and had to climb toward a bottle placed at the top to drink water. RESULTS: Compared with the ground control, bone mineral density of the left femur increased in the climbing mice at 4 weeks. At 2 and 4 weeks, bone formation rate (BFR/BS) of periosteal surface, the cross-sectional area, and moment of inertia were increased in the climbing mice, whereas BFR/BS and eroded surface (ES/BS) of endosteal surface did not differ. The trabecular bone volume (BV/TV) of the proximal tibia increased in climbing mice, and osteoclast surface (Oc.S/BS) and osteoclast number decreased at 2 weeks. At 4 weeks, there were increases in BV/TV and parameters of bone formation, including mineralized surface, mineral apposition rate, and bone formation rate. In marrow cell cultures from the tibia, the number of alkaline phosphatase+ colony forming units-fibroblastic and the area of mineralized nodule formation in climbing mice were increased, and the number of osteoclast-like TRACP+ multinucleated cells was lower at 2 weeks. At 4 weeks, these parameters recovered to the levels of the ground controls. CONCLUSION: Our results indicate that climbing increased trabecular bone volume and reduced bone resorption, with a subsequent increase in bone formation. Intermittent climbing downregulates marrow osteoclastogenic cells and upregulates osteogenic cells initially, but further exercise seemed to desensitize them. Cortical envelopes were enlarged earlier, but the response seems to differ from trabecular bone.  相似文献   
10.
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