全文获取类型
收费全文 | 186491篇 |
免费 | 14826篇 |
国内免费 | 13637篇 |
出版年
2024年 | 240篇 |
2023年 | 2024篇 |
2022年 | 4007篇 |
2021年 | 8668篇 |
2020年 | 5872篇 |
2019年 | 7328篇 |
2018年 | 7150篇 |
2017年 | 5352篇 |
2016年 | 7588篇 |
2015年 | 11034篇 |
2014年 | 13025篇 |
2013年 | 13910篇 |
2012年 | 16797篇 |
2011年 | 15253篇 |
2010年 | 9527篇 |
2009年 | 8431篇 |
2008年 | 9908篇 |
2007年 | 8937篇 |
2006年 | 7905篇 |
2005年 | 6266篇 |
2004年 | 5442篇 |
2003年 | 4876篇 |
2002年 | 4227篇 |
2001年 | 3652篇 |
2000年 | 3387篇 |
1999年 | 3314篇 |
1998年 | 1893篇 |
1997年 | 2000篇 |
1996年 | 1809篇 |
1995年 | 1652篇 |
1994年 | 1602篇 |
1993年 | 1208篇 |
1992年 | 1731篇 |
1991年 | 1381篇 |
1990年 | 1042篇 |
1989年 | 962篇 |
1988年 | 810篇 |
1987年 | 715篇 |
1986年 | 617篇 |
1985年 | 640篇 |
1984年 | 359篇 |
1983年 | 335篇 |
1982年 | 231篇 |
1981年 | 192篇 |
1980年 | 162篇 |
1979年 | 189篇 |
1978年 | 127篇 |
1977年 | 118篇 |
1975年 | 112篇 |
1974年 | 126篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
中国两种掌突蟾(锄足蟾科Pelobatidae,无尾目Anura)的细胞遗传学研究 总被引:1,自引:0,他引:1
本文对分布于云南境内的两种Leptolalax——L.ventripunctatus和L.alpinus的常规Giemsa核型、C-带和Ag-NORs作了研究,结果表明L.ventripunctatus的2n=22,20M 2T,NF=42,1对Ag-NORs位于5(?),并呈现异形现象,该区域亦显C-带正染;L.alpinus 2n=24,14M 4SM 6T,NF=42,1对Ag-NORs位于No.8短臂端部,并有随体联合现象。两种的着丝点区域均呈现C-带正染。 相似文献
992.
为了研究染色体畸变与微核形成的关系,本实验用不同浓度的丝裂霉素C(MMC,0.025—0.4μg/ml),处理人外周血淋巴细胞,观察中期染色体畸变与不同细胞周期形成的微核间的关系。获得如下主要结果:(1)MMC诱发的染色体畸变细胞率(ACF),未经培养的G_0期淋巴细胞的微核细胞率(NC-MNCF)以及培养的淋巴细胞的微核细胞率(C-MNCF),在一定剂量范围内均呈剂量依赖性增加,并可用幂回归方程描述;(2)微核形成与染色体畸变全然无关的NC-MNCF,和C-MNCF一样,与ACF呈良好的正相关;(3)用胞质分裂阻滞(CB)法,检测MMC诱发的CB-MNCF,较C-MNCF无显著提高,MNCF/ACF的比值较小,并随着MMC剂量增加从0.15左右降到0.03。所有上述结果表明,不能简单理解微核形成与染色体畸变间的关系,在分裂的细胞群体中,中期染色体畸变可能仅是微核形成的一种来源。 相似文献
993.
用盒式突变和定点突变对大肠杆菌青霉素G酰化酶α亚基177位ser进行了突变研究,结果发现所挑选的突变体均无酶的活力,这一结果可能可以用来解释Ser 177附近肽段和一些青霉素结合蛋白青霉素结合区在一级结构上保持同源性的原因。 相似文献
994.
995.
996.
S Levine D Silage D Henson J Y Wang J Krieg J LaManca S Levy 《Journal of applied physiology》1991,70(5):2311-2321
We describe a triaxial magnetometer (Tri-mag) system, which consists of a transmitter, four sensors, a processing unit, and a personal computer (PC). The Tri-mag processing unit outputs the position of each sensor relative to the transmitter in three orthogonal coordinates, and this information is communicated to the PC. First, we demonstrated that within a defined octant of a sphere in which the center is the transmitter, we can measure radial distances with an accuracy of +/- 1 mm over a range extending from 10 to 70 cm from the transmitter. Second, we recorded the three-dimensional movement of sensors on the anterior and posterior surfaces of the chest wall during maximum voluntary ventilation in four normal men; all sensors were placed in the midsagittal plane of the body. Anterior sensors were located on the sternum at the level of the third intercostal space and at 2 cm above the umbilicus, whereas posterior sensors were located on the posterior spine at the same vertical levels as the anterior sensors. In all subjects the following was found. 1) Both anterior sensors moved anterior and cephalad during inspiration. The anterior thoracic sensor showed greater vertical than anteroposterior (A-P) movement, whereas the anterior abdominal sensor showed greater A-P than vertical movement. 2) Inspiration was associated with spinal extension, whereas expiration was associated with spinal flexion. Third, we used Tri-mag information to 1) measure tidal volume (VT) over a range extending from 500 ml to inspiratory capacity and 2) measure the change in end-expiratory lung volume (EELV) over a range extending from FRC to FRC plus a minimum of 1.5 liters. Our results indicate that greater than 96% of the changes in VT and greater than 82% of the changes in EELV can be accounted for by changes in A-P, vertical, and lateral dimensions of the chest wall. 相似文献
997.
中国家猪高分辨G—带及模式图 总被引:9,自引:0,他引:9
采用氨甲喋呤或胸苷阻断法使细胞分裂同步化,并结合胰酶G-带技术,对中国7个家猪品种高分辨G-带进行了研究,发现家猪品种间带型基本一致,从而参照人类细胞遗传学命名法的国际体制,提出了中国家猪高分辨G-带标准化核型及模式图,对显带核型界标进行了少许修改,对每对染色体进行了区带划分和描述。单倍染色体组所显示的G-带数目,包括X和Y染色体,巳达444条,近于中期染色体带纹数目的两倍。 相似文献
998.
999.
1000.
Well functioning pulmonary surfactant is necessary to ensure alveolar stability. It is proposed that surfactant is also required to keep the finest cylindrical airways open, thereby securing an unrestricted flow of air to and from the alveoli. If the surfactant is inadequate in quality or quality there is a risk that liquid will accumulate in the most marrow section of the airway and form a blocking column. To study that possibility special glass capillaries were used. The glass capillaries were heated and extended to make a short section very narrow. In the lumen of that section a minute volume (1 microliter) of liquid was deposited, which formed a blocking column. When pressure was raised on one side of the column, it forced the liquid to move away from the narrow section. Pressure dropped to zero as air could pass, and if the liquid column consisted of calf lung surfactant extract (CLSE), pressure remained at zero because a new liquid column did not form. If, on the other hand, the liquid column consisted of saline solution it would repeatedly reform as soon as it had been pressed out of the capillary's narrow section. The same occurred if the CLSE suspension forming the liquid column was very dilute or contained inhibiting proteins. These observations did not require that the capillary consisted of the material glass; they were also noted when the narrow tube was outlined by epithelium. 相似文献