全文获取类型
收费全文 | 532581篇 |
免费 | 59581篇 |
国内免费 | 348篇 |
专业分类
592510篇 |
出版年
2018年 | 5218篇 |
2017年 | 5083篇 |
2016年 | 6940篇 |
2015年 | 8757篇 |
2014年 | 10475篇 |
2013年 | 15236篇 |
2012年 | 16946篇 |
2011年 | 17329篇 |
2010年 | 11689篇 |
2009年 | 10727篇 |
2008年 | 15135篇 |
2007年 | 15690篇 |
2006年 | 14656篇 |
2005年 | 14049篇 |
2004年 | 13907篇 |
2003年 | 13266篇 |
2002年 | 12796篇 |
2001年 | 28354篇 |
2000年 | 28209篇 |
1999年 | 21973篇 |
1998年 | 6722篇 |
1997年 | 7300篇 |
1996年 | 6732篇 |
1995年 | 6210篇 |
1994年 | 5980篇 |
1993年 | 5957篇 |
1992年 | 17044篇 |
1991年 | 16288篇 |
1990年 | 15699篇 |
1989年 | 15214篇 |
1988年 | 13921篇 |
1987年 | 12938篇 |
1986年 | 12040篇 |
1985年 | 11813篇 |
1984年 | 9659篇 |
1983年 | 8081篇 |
1982年 | 5993篇 |
1981年 | 5372篇 |
1980年 | 5097篇 |
1979年 | 8941篇 |
1978年 | 6809篇 |
1977年 | 6273篇 |
1976年 | 5646篇 |
1975年 | 6235篇 |
1974年 | 6760篇 |
1973年 | 6540篇 |
1972年 | 5978篇 |
1971年 | 5428篇 |
1970年 | 4679篇 |
1969年 | 4401篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
S Wongratanacheewin W Rattanasiriwilai R Priwan S Sirisinha 《Journal of helminthology》1987,61(2):151-156
Hamsters experimentally infected with Opisthorchis viverrini had significant depression of the antibody response to sheep red blood cells. The depression was more severe with prolonged infections. Lymphoproliferative response to phytohaemagglutinin stimulation was also depressed when compared with uninfected controls. The immunodepression in these animals was abolished by anthelmintic treatment, suggesting that the immunodepressive effect is reversible and is associated with active infection. 相似文献
102.
A synthetic peptide homologous to the envelope proteins of retroviruses inhibits monocyte-mediated killing by inactivating interleukin 1 总被引:9,自引:0,他引:9
E S Kleinerman L B Lachman R D Knowles R Snyderman G J Cianciolo 《Journal of immunology (Baltimore, Md. : 1950)》1987,139(7):2329-2337
The synthetic peptide CKS-17 has homology to a highly conserved region of the immunosuppressive retroviral envelope protein P15E, to envelope proteins of HTLV I, II, III, and to that encoded by an endogeneous C-type human retroviral DNA. CKS-17 inhibits the immune response of lymphocytes and the respiratory burst of human monocytes. Because P15E-related antigens are present in human malignant cell lines and cancerous effusions, we sought to determine the effect of CKS-17 on monocyte-mediated tumor cell lysis. Lysis of A375 tumor cells by lymphokine or lipopolysaccharide-activated human monocytes was inhibited by 10 microM CKS-17 (control, 79%; CKS-17-treated, 19%). Another synthesized peptide, CS-2, which has partial homology to CKS-17, failed to block monocyte-mediated killing. Thus, the inhibition by CKS-17 appeared to be specific. Because interleukin 1 (IL-1) is a cytocidal factor produced by activated monocytes, we also investigated the effect of CKS-17 on IL-1 production by monocytes and on direct IL-1-mediated cytotoxicity. CKS-17 did not block production or secretion of IL-1 by lipopolysaccharide- or interferon-gamma-activated monocytes. However, the direct cytocidal activity of both recombinant IL-1 alpha and IL-1 beta against A375 tumor cells was blocked by CKS-17. The cytotoxic activity of IL-1 was inhibited by CKS-17 if (a) IL-1 was preincubated with CKS-17 for 1 hr at 37 degrees C or (b) the A375 cells were incubated with CKS-17 for 1 hr prior to the addition of IL-1. CKS-17 also blocked IL-1-induced proliferation of murine thymocytes, the D10 T cell line, and an IL-1-responsive astrocytoma cell line. These data suggest that CKS-17 may be a potent inhibitor of IL-1. 相似文献
103.
Murine monoclonal antibodies to the myelin-associated glycoprotein (MAG) recognize Leu-7-reactive molecules on human mononuclear cells 总被引:2,自引:0,他引:2
M Arai M Nishizawa T Inuzuka M Tanaka H Baba S Sato T Miyatake 《Journal of immunology (Baltimore, Md. : 1950)》1987,138(10):3259-3263
It is known that the antibody to human myelin-associated glycoprotein (MAG) reacts with a subset of human mononuclear cells (MNC) mediating a natural killer (NK) activity. The properties of the target molecule of the anti-MAG antibody, however, have not yet been elucidated. Three (GC-J4, MC-P2, and MC-P4) of five murine monoclonal antibodies (mAb) to MAG bound to human MNC. Moreover, MC-P2 and MC-P4 inhibited the binding of 125I-labeled anti-Leu-7 to MNC in a dose-dependent fashion. Conversely, anti-Leu-7 inhibited the binding of MC-P2 and MC-P4 to MNC, but did not inhibit the binding of GC-J4. Therefore, it is possible that MC-P2 and MC-P4 bind directly to or close to the Leu-7 epitope, and that GC-J4 binds to the epitope which is distinct from the Leu-7 epitope. The electrophoretic patterns of immunoprecipitates with GC-J4, MC-P2 and anti-Leu-7 from detergent lysates of surface-labeled human MNC were very similar. The target molecules of anti-Leu-7 and anti-MAG mAb have apparent m.w. of 205, 170, 150, 135, 110, 85, 65, and 55 kDa. All of the molecules precipitated by these mAb are monomeric or noncovalently associated proteins, because the electrophoretic mobilities of the proteins remained unchanged whether the samples were reduced or not. MC-P4 may have a higher affinity for the 65 kDa molecule than the other mAb, and precipitates the 58 kDa molecule as well. Therefore, the fine antigenic specificity of MC-P4 is slightly different from those of anti-Leu-7 or MC-P2. The implication of these results is that mAb, whose specificity is directed to the carbohydrate part of human MAG, reacts with the Leu-7 reactive molecules on human MNC, and that at least two epitopes detected by anti-MAG mAb coexist on the surface molecules with various apparent m.w. 相似文献
104.
105.
Effect of Quinolinic Acid in the Nucleus Basalis Magnocellularis on Cortical High-Affinity Choline Uptake 总被引:2,自引:2,他引:0
R. H. Metcalf R. J. Boegman R. Quirion R. J. Riopelle S. K. Ludwin 《Journal of neurochemistry》1987,49(2):639-644
A transient 45% increase in cortical high-affinity choline uptake (HACU) was observed after an injection of quinolinic acid (QUIN) into the nucleus basalis magnocellularis (nbM) of the rat. This was followed by a steady decline in choline uptake, which resulted in a 46% decrease by day 7. Specific [3H]hemicholinium-3 binding to coronal brain sections showed a similar pattern following injections of QUIN into the nbM. The increase in cortical HACU elicited by QUIN appeared to be dose dependent. 相似文献
106.
Measurement of Acetylcholine Release in Freely Moving Rats by Means of Automated Intracerebral Dialysis 总被引:15,自引:13,他引:2
G. Damsma B. H. C. Westerink J. B. de Vries C. J. Van den Berg A. S. Horn 《Journal of neurochemistry》1987,48(5):1523-1528
The present study demonstrates the feasibility of measuring acetylcholine in perfusion samples collected by means of in vivo brain dialysis in the striata of freely moving rats. The output of the dialysis device was directly connected to an automated sample valve of a HPLC-assay system that comprises a cation exchanger, a post-column enzyme reactor, and an electrochemical detector. The presence of an acetylcholinesterase inhibitor (neostigmine) in the perfusion fluid was required for the detection of acetylcholine in the perfusate. Increasing concentrations of neostigmine induced increasing amounts of acetylcholine. Continuous perfusion with a fixed concentration (2 microM) of neostigmine resulted in gradually increasing amounts of collected acetylcholine over time although a considerable variation between successive samples exists. The brain dialysis technique was further validated by studying the effect of various drugs. Systemically administered atropine increased the output of acetylcholine, whereas the addition of tetrodotoxin to the perfusion fluid resulted in a complete disappearance of the neurotransmitter. 相似文献
107.
A R Yobs A E Plott M D Hicklin S A Coleman W W Johnston P R Ashton I F Rube J C Watts Z M Naib R J Wood 《Acta cytologica》1987,31(6):900-910
Two laboratories exchanged and rescreened a large sample of cases with cervicovaginal smears they had consecutively accessioned to examine the reproducibility of gynecologic cytodiagnosis under optimum conditions. At least a "working agreement" (diagnoses within +/- 1 category on a ten-category scale) was achieved in diagnoses of normal, benign reaction and squamous abnormality (from minimal dysplasia though invasive cancer) in 18,859 cases (96.8%), of endometrial abnormality in 21 cases (42%) and of "unsatisfactory" in 99 cases (20.7%). Larger differences occurred in greater than or equal to 30% of cases except in the categories of "normal" and "benign reaction," reaching a maximum of 82% for moderate dysplasia. Reexamining 382 cases decreased disagreement by category to the 20% to 65% range only in the five categories of dysplasia plus carcinoma in situ. Agreement was not predicated on the presence of endocervical cells or squamous metaplasia; the basis for "unsatisfactory" calls was not uniform. Comparison of the laboratories' diagnoses with referee diagnoses or, on 178 cases, with tissue diagnoses also demonstrated differences in diagnostic criteria. 相似文献
108.
Multipoint mapping studies of six loci on chromosome 11 总被引:1,自引:0,他引:1
D A Meyers T H Beaty N E Maestri S D Kittur S E Antonarakis H H Kazazian 《Human heredity》1987,37(2):94-101
The six loci, beta-globin (HBBC), parathyroid hormone (PTH), oncogene c-Ha-ras-1 (HRAS1), insulin (INS), calcitonin (CAL) and catalase (CAT) loci, have been mapped to 11p in the order: CAT-CAL-PTH-HBBC-(HRAS1-INS). The purpose of the current study was to examine the linkage relationships, especially the multipoint relationships of these loci in detail. In the 18 families studied, a significant sex difference in recombination was found for the HBBC: HRAS1 linkage with more recombination in the male parent than the female parent (22 vs. 2%). The results of the multipoint analyses provided further evidence for the order CAT-CAL-PTH-HBBC-(HRAS1-INS); however, the order of the last two tightly linked loci is still not clear. 相似文献
109.
From ovulation to oviposition, the corpora lutea of the oviparous lizards Crotaphytus collaris and Eumeces obsoletus exhibit three stages of luteal development: 1) luteogenesis, 2) luteal maturity, and 3) luteal regression. Each stage exhibits distinct characteristics, involving changes in: 1) luteal volume, 2) nuclear diameter of cells within the luteal cell mass, and 3) thecal development. Plasma progesterone concentration is greatest during luteogenesis and is positively correlated with ovarian atresia, although atresia occurred throughout the period of gravidity. These data suggest that in these two species, the corpora lutea secrete high amounts of progesterone immediately following ovulation and exhibit morphologically distinct stages of growth and regression. 相似文献
110.
D K Whittaker S Ryan K Weeks W M Murphy 《American journal of physical anthropology》1987,73(3):389-396
The approximal surfaces of premolars and molars of 376 adult British-Romano skulls were examined for wear facets. The type of wear was designated as convex, concave, sigmoid, or flat, and the degree was categorised on a three-point scale. Concave wear facets were more frequently seen in the older age groups, but the type of wear was similar on right and left sides. Taking all teeth together or as individual tooth types, concave wear was significantly more likely on mesial rather than distal surfaces. The degree of wear was age related and similar on right and left sides in both males and females. It is suggested that the distribution of concave facets may be related to movements between adjacent teeth. 相似文献