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   4182篇
  免费   461篇
  国内免费   19篇
耳鼻咽喉   37篇
儿科学   212篇
妇产科学   65篇
基础医学   711篇
口腔科学   120篇
临床医学   469篇
内科学   773篇
皮肤病学   41篇
神经病学   295篇
特种医学   157篇
外科学   617篇
综合类   85篇
一般理论   1篇
预防医学   397篇
眼科学   95篇
药学   197篇
中国医学   4篇
肿瘤学   386篇
  2021年   57篇
  2020年   28篇
  2019年   55篇
  2018年   75篇
  2017年   42篇
  2016年   50篇
  2015年   79篇
  2014年   81篇
  2013年   137篇
  2012年   194篇
  2011年   208篇
  2010年   89篇
  2009年   80篇
  2008年   175篇
  2007年   189篇
  2006年   192篇
  2005年   163篇
  2004年   143篇
  2003年   148篇
  2002年   149篇
  2001年   120篇
  2000年   143篇
  1999年   126篇
  1998年   68篇
  1997年   72篇
  1996年   49篇
  1995年   64篇
  1994年   43篇
  1993年   50篇
  1992年   103篇
  1991年   109篇
  1990年   92篇
  1989年   115篇
  1988年   96篇
  1987年   93篇
  1986年   87篇
  1985年   81篇
  1984年   50篇
  1983年   57篇
  1982年   58篇
  1981年   41篇
  1980年   34篇
  1979年   57篇
  1978年   38篇
  1977年   32篇
  1976年   49篇
  1975年   41篇
  1974年   42篇
  1973年   44篇
  1972年   35篇
排序方式: 共有4662条查询结果,搜索用时 15 毫秒
61.
Background: Five of the most abundant human milk oligosaccharides (HMOs) in human milk are 2′-fucosyllactose (2′-FL), 3-fucosyllactose (3-FL), lacto-N-tetraose (LNT), 3′-sialyllactose (3′-SL) and 6′-sialyllactose (6′-SL). Methods: A randomized, double-blind, controlled parallel feeding trial evaluated growth in healthy term infants fed a control milk-based formula (CF; n = 129), experimental milk-based formula (EF; n = 130) containing five HMOs (5.75 g/L; 2′-FL, 3-FL, LNT, 3′-SL and 6′-SL) or human milk (HM; n = 104). Results: No significant differences (all p ≥ 0.337, protocol evaluable cohort) were observed among the three groups for weight gain per day from 14 to 119 days (D) of age, irrespective of COVID-19 or combined non-COVID-19 and COVID-19 periods. There were no differences (p ≥ 0.05) among the three groups for gains in weight and length from D14 to D119. Compared to the CF group, the EF group had more stools that were soft, frequent and yellow and were similar to the HM group. Serious and non-serious adverse events were not different among groups, but more CF-fed infants were seen by health care professionals for illness from study entry to D56 (p = 0.044) and D84 (p = 0.028) compared to EF-fed infants. Conclusions: The study demonstrated that the EF containing five HMOs supported normal growth, gastrointestinal (GI) tolerance and safe use in healthy term infants.  相似文献   
62.
Summary (1) Plasma protein binding of salicylate was studied in 14 patients with cutaneous hepatic porphyria (CHP) and 11 normal subjects using ultrafiltration with centrifugation (membrane cones) and continuous ultrafiltration. (2) Albumin and haemoglobin levels were significantly reduced in patients with CHP, and salicylate binding by ultrafiltration/centrifugation was 65% compared with 84% in normal subjects. (3) Plasma porphyrin levels were raised, but did not correlate with salicylate binding, and protoporphyrin or uroporphyrin added to plasma did not alter the amount of drug bound. (4) Palmitate added to plasma reduced salicylate binding by 9 to 20% but a crossover of patient and normal plasma proteins and ultrafiltrates confirmed that no other ultrafiltrable metabolites present in patient plasma appeared to cause decreased binding. (5) Scatchard plots obtained by continuous ultrafiltration for normal and patient plasma showed a reduction in the number of primary and secondary binding sites and an increase in the intrinsic association constants for both these sites. (6) It was concluded that the decreased salicylate binding in CHP was due to a reduced albumin concentration and altered salicylate albumin interaction.  相似文献   
63.
Summary The protein binding of methotrexate by serum from eight normal volunteers was assessed by continuous ultrafiltration at pH 7.4 and 37°C. Methotrexate concentrations were measured by radioimmunoassay and the data analysed by the method of Scatchard. The major binding protein was albumin which bound 87.3% of the drug in serum. Analysis of the Scatchard plots indicated two distinct groups of binding sites. Class I was found to have 0.16±0.05 (S D) binding sites with an intrinsic association constant of 71.15±35.98 (S D)×104 M–1: Class II had 2.01±0.93 (S D) binding sites and an affinity of 0.18±0.15×104 M–1. No great change in the percentage of methotrexate bound occurred until the total concentration of the drug exceeded 50 µMol 1–1.  相似文献   
64.
1. Studies have been made of the behavior of renal blood flow after partial constriction of the renal artery in twenty-four dogs. 2. When reduction in renal blood flow is produced by partial constriction of the renal artery, a readjustment of flow in the direction of normal occurs within a few minutes, subsequent constriction being again followed by a return of flow toward normal until the artery is markedly constricted. 3. Renal blood flow after marked constriction of the artery becomes extremely susceptible to the vasoconstrictive action of small doses of adrenalin, and flow may cease with larger doses for a considerable period of time. 4. Arterial hypertension of significant degree may follow partial constriction of one renal artery during brief experiments when adrenalin in addition has been administered. 5. Further evidence is presented in favor of the concept that the renal circulation enjoys a control independent of systemic arterial pressure.  相似文献   
65.
Technological advancements are dramatically changing the landscape of therapeutic development. The convergence of advances in computing power, analytical methods, artificial intelligence, novel digital health tools, and cloud‐based platforms has the potential to power an exponential acceleration of evidence generation. For regulatory agencies responsible for evidence evaluation and oversight of medical products, these advances present both promises and challenges. Ultimately, realizing the translation and impact of these innovations that could potentially enhance therapeutic development and improve the health of individuals and the public will require a nimble and responsive regulatory approach. Supporting an adaptive policy‐making infrastructure that is poised to address novel regulatory considerations, creating a workforce to ensure relevant expertise, and fostering more diverse collaborations with a broader group of stakeholders are steps toward the goal of modernizing the regulatory ecosystem. This article outlines approaches that can help provide the flexibility and tools needed to foster innovation, while ensuring the safety and effectiveness of medical products.  相似文献   
66.
67.
We have studied the effects of sulfasalazine and its metabolites on cell-mediated cytotoxicity by peripheral blood and intestinal mononuclear cells from both control and inflammatory bowel disease (IBD) patients. Sulfasalazine and sulfapyridine, as well as hydrocortisone and nordihydroguaiaretic acid inhibited spontaneous cell-mediated cytotoxicity by control and IBD peripheral blood cells. Sulfasalazine and nordihydroguaiaretic acid inhibited spontaneous cell-mediated cytotoxicity by control and IBD intestinal mononuclear cells cultured for 72 h in media alone. In contrast, 5-aminosalicylate, indomethacin and benzylimidazole had no effect on cytotoxicity by any cell population. Lectin-induced, antibody-dependent and interleukin-2-induced cell-mediated cytotoxicity, as well as lymphokine-activated killing were not inhibited by the drugs: inhibitory effects in these assays were primarily upon the underlying spontaneous cell-mediated cytotoxicity. The inhibition induced by sulfasalazine, sulfapyridine and nordihydroguaiaretic acid could not be reversed by adding the lipoxygenase metabolites leukotriene B4 or 12-hydroxyeicosatetraenoic acid. These findings demonstrate that spontaneous cell-mediated cytotoxicity by control and IBD mononuclear cells can be inhibited by sulfasalazine.  相似文献   
68.
An epidemic form of arthritis has been occurring in eastern Connecticut at least since 1972, with the peak incidence of new cases in the summer and early fall. Its identification has been possible because of tight geographic clustering in some areas, and because of a characteristic preceding skin lesion in some patients. The authors studied 51 residents of three contiguous Connecticut communities—39 children and 12 adults—who developed an illness characterized by recurrent attacks of asymmetric swelling and pain in a few large joints, especially the knee. Attacks were usually short (median: 1 week) with much longer intervening periods of complete remission (median: 2.5 months), but some attacks lasted for months. To date the typical patient has had three recurrences, but 16 patients have had none. A median of 4 weeks (range: 1–24) before the onset of arthritis, 13 patients (25%) noted an erythematous papule that developed into an expanding, red, annular lesion, as much as 50 cm in diameter. Only 2 of 159 family members of patients had such a lesion and did not develop arthritis (P < 0.000001). The overall prevalence of the arthritis was 4.3 cases per 1,000 residents, but the prevalence among children living on four roads was 1 in 10. Six families had more than 1 affected member. Nine of 20 symptomatic patients had low serum C3 levels, compared to none of 31 asymptomatic patients (P < 0.005); no patient had iridocyclitis or a positive test for antinuclear antibodies. Neither cultures of synovium and synovial fluid nor serologic tests were positive for agents known to cause arthritis. “Lyme arthritis” is thought to be a previously unrecognized clinical entity, the epidemiology of which suggests transmission by an arthropod vector.  相似文献   
69.
Summary The in vivo bending rigidity and bone mineral content of monkey ulnae and tibiae were measured. Bending rigidity in the anteroposterior plane was measured by an impedance probe technique. Forced vibrations of the bones were induced with an electromechanical shaker, and force and velocity at the driving point were determined. The responses over the range of 100–250 Hz were utilized to compute the bending rigidity. Bone mineral content in the cross section was determined by a photon absorption technique. Seventeen male monkeys (Macaca nemestrina) weighing 6–14 kg were evaluated. Repeatability of the rigidity measures was 4%. Bone mineral content was measured with a precision of 3.5%. Bending rigidity was correlated with the mineral content of the cross section,r=0.899. Two monkeys were evaluated during prolonged hypodynamic restraint. Restraint produced regional losses of bone most obviously in the proximal tibia. Local bone mineral content declines 17 to 24% and the average bending rigidity declines 12 to 22%. Changes in bones leading to a reduction in mineral content and stiffness are discussed.  相似文献   
70.
Sixty-nine patients have been followed prospectively after curative resection of Dukes-Kirklin B-2 or C colorectal cancer. Serial plasma samples were studied in selected patients to determine changes in circulating immune complex concentrations (CIC) following primary tumor resection, and to compare serial plasma CIC and carcinoembryonic antigen (CEA) levels. CIC was determined in an average of seven serial samples per patient by inhibition of antibody-dependent cell-mediated cytotoxicity (ADCC). CEA assays were performed by the Hanson Z-gel method. Two distinct patterns of serial CIC have emerged. In seven patients with no known tumor recurrences, serial CEA levels and CIC oscillated regularly and were inversely related. In seven of eight patients whose tumors recurred, both CEA and CIC rose together. In three patients with elevated plasma CEA levels due to inflammatory bowel disease, serial Ag-Ab complex concentrations did not vary, nor did separated Ag or Ab fractions inhibit ADCC. These data suggest that, in patients following curative resection of colorectal cancer, serial changes in circulating immune complexes may discriminate between transient CEA elevations which occur despite no known tumor recurrence and tumor recurrence which is beyond the capacity of adequate host antitumor defense.  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