全文获取类型
收费全文 | 3091篇 |
免费 | 228篇 |
国内免费 | 20篇 |
专业分类
耳鼻咽喉 | 39篇 |
儿科学 | 179篇 |
妇产科学 | 30篇 |
基础医学 | 308篇 |
口腔科学 | 94篇 |
临床医学 | 343篇 |
内科学 | 520篇 |
皮肤病学 | 76篇 |
神经病学 | 348篇 |
特种医学 | 366篇 |
外科学 | 338篇 |
综合类 | 72篇 |
预防医学 | 170篇 |
眼科学 | 33篇 |
药学 | 125篇 |
1篇 | |
肿瘤学 | 297篇 |
出版年
2020年 | 22篇 |
2019年 | 32篇 |
2018年 | 52篇 |
2016年 | 37篇 |
2015年 | 44篇 |
2014年 | 70篇 |
2013年 | 113篇 |
2012年 | 80篇 |
2011年 | 94篇 |
2010年 | 90篇 |
2009年 | 86篇 |
2008年 | 83篇 |
2007年 | 102篇 |
2006年 | 100篇 |
2005年 | 92篇 |
2004年 | 80篇 |
2003年 | 74篇 |
2002年 | 72篇 |
2001年 | 72篇 |
2000年 | 61篇 |
1999年 | 100篇 |
1998年 | 104篇 |
1997年 | 90篇 |
1996年 | 82篇 |
1995年 | 72篇 |
1994年 | 55篇 |
1993年 | 58篇 |
1992年 | 57篇 |
1991年 | 81篇 |
1990年 | 52篇 |
1989年 | 86篇 |
1988年 | 78篇 |
1987年 | 74篇 |
1986年 | 67篇 |
1985年 | 78篇 |
1984年 | 55篇 |
1983年 | 44篇 |
1982年 | 37篇 |
1981年 | 33篇 |
1980年 | 44篇 |
1979年 | 51篇 |
1978年 | 52篇 |
1977年 | 42篇 |
1976年 | 35篇 |
1975年 | 35篇 |
1974年 | 34篇 |
1973年 | 30篇 |
1972年 | 23篇 |
1971年 | 33篇 |
1970年 | 37篇 |
排序方式: 共有3339条查询结果,搜索用时 15 毫秒
21.
AJ van Geest† PJM Berretty† PJJM Klinkhamer‡ HAM Neumann§ 《Journal of the European Academy of Dermatology and Venereology》2002,16(5):529-531
BACKGROUND: Acquired cerebriform intradermal naevus (CIN) is a rare form of pseudo cutis verticis gyrata. CASE REPORT: A case of acquired CIN of the scalp in a 46-year-old male patient is presented. The clinical and histopathological presentations of CIN are described and the therapeutic possibilities are discussed. CONCLUSIONS: In each individual case the physician must decide whether to do surgery or follow a wait-and-see policy. There is little risk of malignant change of CIN, and surgical excision of such lesions often involves evident mutilation. 相似文献
22.
Stabilization of phage T4 lysozyme by engineered disulfide bonds. 总被引:14,自引:2,他引:12
M Matsumura W J Becktel M Levitt B W Matthews 《Proceedings of the National Academy of Sciences of the United States of America》1989,86(17):6562-6566
Four different disulfide bridges (linking positions 9-164, 21-142, 90-122, and 127-154) were introduced into a cysteine-free phage T4 lysozyme at sites suggested by theoretical calculations and computer modeling. The new cysteines spontaneously formed disulfide bonds on exposure to air in vitro. In all cases the oxidized (crosslinked) lysozyme was more stable than the corresponding reduced (noncrosslinked) enzyme toward thermal denaturation. Relative to wild-type lysozyme, the melting temperatures of the 9-164 and 21-142 disulfide mutants were increased by 6.4 degrees C and 11.0 degrees C, whereas the other two mutants were either less stable or equally stable. Measurement of the equilibrium constants for the reduction of the engineered disulfide bonds by dithiothreitol indicates that the less thermostable mutants tend to have a less favorable crosslink in the native structure. The two disulfide bridges that are most effective in increasing the stability of T4 lysozyme have, in common, a large loop size and a location that includes a flexible part of the molecule. The results suggest that stabilization due to the effect of the crosslink on the entropy of the unfolded polypeptide is offset by the strain energy associated with formation of the disulfide bond in the folded protein. The design of disulfide bridges is discussed in terms of protein flexibility. 相似文献
23.
Bob Mash Di Powell Felicity du Plessis Unita van Vuuren Margaret Michalowska Naomi Levitt 《Suid-Afrikaanse tydskrif vir geneeskunde》2007,97(12):1284-1288
BACKGROUND AND AIMS: In South Africa diabetes makes a significant contribution to the burden of disease. Diabetic retinopathy is a leading cause of adult blindness, and screening can reduce the incidence. This project aimed to implement and evaluate a new service for retinal screening that uses a non-mydriatic mobile fundal camera in primary care. This is the first time such a service has been evaluated in an African primary care context. METHODS: The service was implemented as an operational research study at three community health centres and data were collected to evaluate the operational issues, screening, reporting and referral of patients. RESULTS: Out of 400 patients screened 84% had a significantly reduced visual acuity, 63% had retinopathy (22% severe nonproliferative, 6% proliferative and 15% maculopathy), 2% of eyes could not be screened and 14% of patients required dilatation. Referral was necessary in 27% of cases for cataracts, in 7% for laser treatment and in 4% for other specialist services. Repeat photography was needed in 8% and urgent follow-up in 12%. A SWOT analysis of the pilot project was completed and recommendations were made on how to integrate it into the district health system. CONCLUSION: Screening with a fundal camera improved the quality of care for diabetic patients and is feasible in the South African public sector, primary care setting. A single technician should be able to photograph almost 10,000 patients a year. 相似文献
24.
AE Boothroyd BVS Murthy A Darbyshire AJ Petros 《Acta paediatrica (Oslo, Norway : 1992)》1996,85(12):1422-1425
Objective: Right upper lobe collapse is a common radiographic finding in intubated children. We hypothesized that deep suctioning and uncontrolled negative pressures during endotracheal tube suctioning were significant contributory factors. Methods : The incidence of right upper lobe (RUL) collapse in intubated, ventilated children on a paediatric cardiac intensive care unit was determined over a 3-month period ( n = 102). Graduated suction catheters and suction vacuums of < 165 cm H2 O were then introduced. Another prospective audit was carried out 3 months later ( n = 60). Results : We found that 24% developed RUL collapse and 4 developed an apical pneumothorax. Following the introduction of graduated catheters and controlled vacuums pressures, a significant reduction in the incidence of RUL collapse, to 7%, was observed ( p < 0.05). Conclusions : We conclude that high negative pressure and deep-suctioning causes RUL collapse in children. Any lobar collapse not only prolongs the child's stay in intensive care, but can be associated with further morbidity which may have a serious implication. By improving suctioning technique this morbidity can be significantly reduced. 相似文献
25.
A carbohydrate differentiation antigen (CDA-3C2) exhibits a highly specific and restricted pattern of expression during rat embryogenesis. In the periphery of the embryo, this antigen is associated transiently with the lateral ectoderm but is retained only in the olfactory and otic epithelium throughout morphogenesis. At the light microscopic level, CDA-3C2 immunoreactivity appears mostly along cell periphery and in the extracellular matrix. The aim of the present study was to determine the specific cellular and subcellular distribution of CDA-3C2 in vivo in order to identify potential sites of cellular and tissue function of the antigen during embryogenesis. There was a strikingly similar subcellular distribution of CDA-3C2 in the developing otic and olfactory systems, found mostly along cell membranes, microvillar projections and acellular secretions of the epithelium. Mature sensory components of the epithelia were not immunoreactive, whereas supportive cells and their secreted structures were densely stained. The highly coincident nature of CDA-3C2 in both sensory epithelia suggests that this carbohydrate epitope, and possibly its carrier macromolecule, participate in a morphogenetic function common to these two sensory epithelia. © Wiley-Liss, Inc. 相似文献
26.
Verschuren MC; Blom B; Bogers AJ; Spits H; van Dongen JJ 《International immunology》1998,10(12):1873-1880
Recombination of deltaRec to psiJalpha will delete the TCR delta gene,
which is thought to play an important role in the bifurcation of the TCR
alphabeta versus TCR gammadelta differentiation lineages. We recently
detected a DNA-binding protein in human thymocytes, the so- called PJA-BP,
which recognizes the psiJalpha gene segment and might be one of the factors
involved in the regulation of preferential deltaRec- psiJalpha
rearrangements. We now investigate PJA-BP expression and its correlation
with TCR delta gene deletion in thymocytes. Our electrophoretic mobility
shift assay experiments showed that the PJA-BP is evolutionary conserved in
human, murine and simian thymocytes. Using a large series of human
hematopoietic malignancies (n = 30), we conclude that PJA-BP expression is
thymocyte specific and seems to be restricted to thymocytes committed to
the TCR alphabeta lineage. Analysis of seven well-defined human thymocyte
subpopulations showed that preferential deltaRec-psiJalpha rearrangements
as well as PJA-BP expression can be detected from the immature
CD34-/CD1+/CD3- /CD4+/CD8alpha+beta- thymocyte differentiation stage
onwards. These experiments indicate that expression of PJA-BP in human
thymocytes starts simultaneously with preferential deltaRec-psiJalpha
rearrangements, which supports our hypothesis that PJA-BP is one of the
factors involved in the preferential recombination of deltaRec to
psiJalpha.
相似文献
27.
Chlamydia trachomatis stimulates human peripheral blood B lymphocytes to proliferate and secrete polyclonal immunoglobulins in vitro 总被引:3,自引:4,他引:3 下载免费PDF全文
Infectious Chlamydia trachomatis (LGV strain), obligate intracellular bacteria, stimulated human peripheral blood lymphocytes to proliferate and secrete immunoglobulins in vitro. In contrast, mock-infected preparations were unable to induce similar responses in peripheral blood lymphocytes. Although levels of immunoglobulin secreted into the media of LGV-stimulated cultures were greater than 10 micrograms/ml, we estimated that less than 1% of these molecules were directed against the bacteria itself, suggesting polyclonal antibody production. Since stimulation with Formalin-killed bacteria resulted in comparable numbers of plaque-forming cells (PFC) as infectious particles, we concluded that the polyclonal immunoglobulin response was not dependent on the in vitro chlamydial infectious process. The polyclonal PFC response induced by LGV was highly sensitive to monocyte inhibition. Although LGV induced proliferation of predominantly B cells, the numbers of generated PFC was increased by the addition of autologous T cells. Neither lymphocyte proliferation nor PFC responses of normal human volunteers correlated significantly with the presence or titer of antichlamydial antibodies in their sera. 相似文献
28.
K. Hopayian G. Horrocks P. Garner A. Levitt 《The British journal of general practice》1983,33(253):506-507
The problems of battered women have recently been highlighted. They consult doctors, who can be an important source of help. We examined their initial presenting complaint to general practitioners. Questionnaires were sent to 27 London refuges for battered women and to 100 randomly selected general practitioners. Seventy-two women and 49 doctors replied. The results indicated that these women are more likely to present with psychological symptoms. Many cases are not detected because the battering is concealed. The attitude of doctors may prevent these patients discussing their real problems. Further studies are needed. 相似文献
29.
30.