全文获取类型
收费全文 | 83781篇 |
免费 | 5454篇 |
国内免费 | 2943篇 |
出版年
2024年 | 146篇 |
2023年 | 1287篇 |
2022年 | 1957篇 |
2021年 | 2594篇 |
2020年 | 2546篇 |
2019年 | 3558篇 |
2018年 | 3099篇 |
2017年 | 2197篇 |
2016年 | 2240篇 |
2015年 | 2827篇 |
2014年 | 5249篇 |
2013年 | 6551篇 |
2012年 | 3979篇 |
2011年 | 5255篇 |
2010年 | 4006篇 |
2009年 | 4407篇 |
2008年 | 4519篇 |
2007年 | 4592篇 |
2006年 | 4134篇 |
2005年 | 3615篇 |
2004年 | 3202篇 |
2003年 | 2610篇 |
2002年 | 2325篇 |
2001年 | 1526篇 |
2000年 | 1231篇 |
1999年 | 1264篇 |
1998年 | 1286篇 |
1997年 | 1013篇 |
1996年 | 904篇 |
1995年 | 843篇 |
1994年 | 754篇 |
1993年 | 584篇 |
1992年 | 577篇 |
1991年 | 469篇 |
1990年 | 395篇 |
1989年 | 328篇 |
1988年 | 291篇 |
1987年 | 259篇 |
1986年 | 201篇 |
1985年 | 351篇 |
1984年 | 563篇 |
1983年 | 415篇 |
1982年 | 411篇 |
1981年 | 305篇 |
1980年 | 236篇 |
1979年 | 221篇 |
1978年 | 187篇 |
1977年 | 155篇 |
1976年 | 123篇 |
1975年 | 116篇 |
排序方式: 共有10000条查询结果,搜索用时 18 毫秒
991.
本实验观察到家兔出血性休克时的低血压能被侧脑室(i.c.v.)内注射蛙皮素(BBS)逆转。预先向i.c.v.注射酚妥拉明或奈洛尔均可减弱BBS的抗出血性休克效应,而预先用saralasin或血管升压素拮抗剂对BBS的该作用无明显影响。以上结果提示,脑内注射BBS有明显的抗出血性休克作用,此作用可能是通过脑内肾上腺素能受体(α和β受体)介导的,而似与脑内血管紧张素Ⅱ和血管升压素的释放无关。 相似文献
992.
EB病毒胸苷激酶基因的扩增 总被引:1,自引:0,他引:1
EB病毒胸苷激酶基因的扩增陈尚武,陈瑞君,黄迪,朱振宇,马涧泉(中山医科大学生化教研室,广州510089)(中山医科大学肿瘤研究所,广州510060)关键词Epstein-Barr病毒,胸苷激酶,基因,聚合酶链反应鼻咽癌(nasopharyngeal... 相似文献
993.
固定化酵母细胞生产1,6-二磷酸果糖研究 总被引:2,自引:0,他引:2
本文研究了固定化酵母细胞制备果糖1,6二磷酸(FDP)的方法及其生产。用卡拉胶包埋方法固定化酿酒酵母(Sacchromyces cerevisae),对含葡萄糖1.0M,磷酸盐0.8M的糖磷液,pH6.5,在37℃下进行磷酸化反应。反复分批转化20天以上,可达到平均产FDPH_427.58mg/ml,最高为59.94mg/ml。用100ml固定化细胞生物反应器连续运转309h,稀释速率D=0.097h~(-1),平均产FDPH_4 21.51mg/ml。20L反应器连续运转,生产能力达到1.7g/h.L。用层析方法制备FDPNa_3结晶粉,提取收率为72.08%,制备质量达到或超过了国内外同类产品的质量要求。 相似文献
994.
中药前胡核磁共振氢谱法鉴定 总被引:1,自引:1,他引:0
使用^1H-NMR法对19种前胡乙醚提取物进行了测试和解析,其中9种前胡的化学成分未见报道。根据主要化学成分香豆素的类型,将含角型二氢吡喃香豆素的10种前胡归入白花前胡类;含线型二氢吡喃香豆素或线型二氢呋喃香豆素的8种前胡归秋紫花前胡类。研究结果表明,^1H-NMR法是鉴别中药前胡的快速、简便而可靠的检测方法。 相似文献
995.
人类免疫缺陷病毒1/2型抗体检测酶联免疫试剂盒的研制 总被引:2,自引:0,他引:2
采用二聚体合成肽(HIV-1gp41、gp120、p24和HIV-2gp36)包被酶标板条制备成固相抗原,与鼠抗人IgG单克隆抗体酶标记物、底物TMB及阴阳性参考血清配套制备成HIV抗体EIA试剂盒,专供检测人血清或血浆HIV1/2抗体之用。以荷兰、韩国及万泰试剂作为对照,用该试剂盒对检定所的Panel标准及献血员15550例(其中HCV抗体阳性128例,HBsAg阳性46例)进行检测,四种试剂对检定所Panel标准的13份阳性血清均呈阳性反应,28份阴性血清均为阴性;献血员15550例,四种试剂对其中1份血清均呈阳性反应,经Westernblot试验证实为阴性,四种试剂的阴性检出率均为99.99%。连续制备三批试剂经中国药品生物制品检定所检定,所检项目全部合格;同时委托检定所进行临床考核,47份阳性血清全部呈阳性反应,150份阴性血清全部为阴性。说明该试剂盒具有很好的敏感性和特异性。 相似文献
996.
Herman Yeger Diane Forget Jennifer Alami Bryan R. G. Williams 《In vitro cellular & developmental biology. Animal》1996,32(8):496-504
Summary The temporal and spatial expression patterns of the Wilms tumor gene, WT1, were studied during the organogenesis of the mouse
kidneyin vitro. In situ hybridization and immunocytochemistry localized cellular expression of WT1 in whole kidney organ cultures to the induced
metanephric mesenchyme and developing podocytes. Organ cultures were further characterized immunocytochemically with antibodies
that specifically labeled the different tubular epithelial components and supporting mesenchyme of the developing nephrons.
In organ cultures, the WT1 expression pattern could be visualized in induced metanephric mesenchyme and entire cell cohorts
of differentiating podocytes. Expression of WT1 and cell specific markers were retained in short-term monolayer cultures of
dissociated kidneys. The development of the metanephric kidneyin vitro involves a highly restricted temporal and spatial cellular expression pattern of WT1 which closely follows that observed
in tissue sections from gestational kidney isolated during organogenesis in the mouse. 相似文献
997.
Hongkui Jin Renhui Yang Gilbert A. Keller Anne Ryan Annie Ko David Finkle Todd A. Swanson WeiLi Diane Pennica William I. Wood Nicholas F. Paoni 《Cytokine》1996,8(12):920-926
Cardiotrophin-1 (CT-1) is a recently discovered cytokine that was isolated based on its ability to induce cardiac myocyte hypertrophy in vitro. In this study, the effects of chronic administration of CT-1 to mice (0.5 or 2 μg by intraperitoneal injection, twice a day for 14 days) were determined. A dose-dependent increase in both the heart weight and ventricular weight to body ratios was observed in the treated groups. The body weights of the animals were unaffected. These results indicate that CT-1 can induce cardiac hypertrophy in vivo. CT-1 was not specific for the heart, however. It stimulated the growth of the liver, kidney, and spleen, and caused atrophy of the thymus. CT-1 administration also increased the platelet counts by 70%, with no change in mean platelet volume. Red blood cell counts were increased in the treated animals, and there was a concomitant increase in haemoglobin concentration. Thus, CT-1 has a broad spectrum of biological activities in vivo. This observation is consistent with previous in-vitro findings showing that the mRNA for CT-1 is expressed in several tissues, and that CT-1 can function through binding to the leukaemia inhibitory factor (LIF) receptor and signalling through the gp130 pathway. 相似文献
998.
Joji Sekine Kazuo Sano Masataka Uehara Tsugio Inokuchi 《Biotechnic & histochemistry》1996,71(3):152-156
A technique Is described for rapid detection of S-pha?e cells of tumor tissues in smear specimens using bromodeoxyuridine (BrdU) immunostaining. Mouse NR-S1 tumors and human tumor specimens were prepared for smear cytology after incubation in RPMI 1640 culture medium containing 200 μM BrdU at 37 °C under 3 atm for 1 hr. Samples were fixed in 70% ethanol for 30 min and used immediately or air dried for 30 min. Samples were then denatured in either 4 N HC1 or 0.07 N NaOH to prepare partially single-stranded DMA. Fixation with air drying for 30 min followed by 30 min in 70% ethanol and 1 min denaturation with 0.07 N NaOH resulted in satisfactory staining quality. Cultured tumor specimens were processed for routine paraffin sections after smears were made for cytology. The labeling indices of the smear specimens and of the paraffin sections gave similar results. This technique should be useful in evaluating the cell proliferative potential of tumor tissue in smear cytology without processing paraffin sections. 相似文献
999.
ANIL K. BHUNIA DWIJEN SARKAR PIJUSH K. DAS 《The Journal of eukaryotic microbiology》1996,43(5):373-379
We investigated activation signaling events in bone marrow-derived macrophages after infection with Leishmania donovani, an intracellular parasite of macrophages. Leishmania donovani infection caused a general suppression of activation parameters like O2- and NO production. However, conditions which allow parasite attachment and prevent entry resulted in triggering of O2- and NO production and stimulation of O2 consumption. Optimal NO and O2- production occurred when bone marrow-derived macrophages and Leishmania ratio was 1:100. The activation signal for O2- production was initiated 15 min after parasite attachment, whereas augmentation of NO production started 6 h after attachment. Activation of O2- and NO generation by L. donovani attachment was inhibited by staurosporine as well as by prolonged treatment of phorbol myristate acetate suggesting a protein kinase C-dependent mechanism. Translocation studies showed that protein kinase C activity in cell membrane fraction rapidly and transiently increased following parasite attachment. No such protein kinase C translocation event occurred in L. donovani infected bone marrow-derived macrophages. Phorbol myristate acetate was found to stimulate membrane translocation of protein kinase C in parasite attached cells whereas it was impaired in infected cells. However, both attachment and infection induced a similar shift of phorbol receptors from cytosolic to membrane fraction indicating that in infected cells the translocation of protein kinase C protein was not impaired but the activity of the membrane associated enzyme was somehow inhibited. These results suggest that although internalization of intracellular parasites like L. donovani caused inhibition of nitrite and superoxide release, mere attachment on macrophage surface resulted in an activation of protein kinase C-mediated downstream oxidative events. 相似文献
1000.
CYNTHIA A. HALE MARY ELLEN JACOBS HEATHER G. ESTES SUSMITA GHOSH LAWRENCE A. KLOBUTCHER 《The Journal of eukaryotic microbiology》1996,43(5):389-392
The sequences of a 1.8-kbp macronuclear DNA molecule (V3), and the majority of its micronuclear counterpart, are reported. The macronuclear V3 DNA molecule contains an open reading frame that is interrupted by a single intron, while the micronuclear copy is interrupted by four internal eliminated sequences, one of which is located within the intron. The predicted protein product of the macronuclear V3 gene is a 471-amino acid polypeptide that is very similar to a group of protein-serine/threonine kinases from both plant and animal species, some of whose members appear to be involved in cell cycle or growth control. 相似文献