全文获取类型
收费全文 | 2506篇 |
免费 | 183篇 |
国内免费 | 507篇 |
专业分类
林业 | 176篇 |
农学 | 191篇 |
基础科学 | 541篇 |
618篇 | |
综合类 | 817篇 |
农作物 | 27篇 |
水产渔业 | 39篇 |
畜牧兽医 | 761篇 |
园艺 | 5篇 |
植物保护 | 21篇 |
出版年
2024年 | 7篇 |
2023年 | 35篇 |
2022年 | 61篇 |
2021年 | 70篇 |
2020年 | 68篇 |
2019年 | 98篇 |
2018年 | 57篇 |
2017年 | 126篇 |
2016年 | 115篇 |
2015年 | 104篇 |
2014年 | 117篇 |
2013年 | 121篇 |
2012年 | 167篇 |
2011年 | 162篇 |
2010年 | 116篇 |
2009年 | 130篇 |
2008年 | 96篇 |
2007年 | 165篇 |
2006年 | 164篇 |
2005年 | 218篇 |
2004年 | 175篇 |
2003年 | 105篇 |
2002年 | 82篇 |
2001年 | 77篇 |
2000年 | 80篇 |
1999年 | 72篇 |
1998年 | 66篇 |
1997年 | 47篇 |
1996年 | 51篇 |
1995年 | 42篇 |
1994年 | 35篇 |
1993年 | 30篇 |
1992年 | 24篇 |
1991年 | 22篇 |
1990年 | 29篇 |
1989年 | 15篇 |
1988年 | 16篇 |
1987年 | 7篇 |
1986年 | 7篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1979年 | 1篇 |
排序方式: 共有3196条查询结果,搜索用时 46 毫秒
1.
The presentation, diagnostic evaluation, treatment, and 5 years follow-up of a 12-year-old Arabian-Saddlebred cross gelding with neck pain and stiffness, attributable to a fracture of the third cervical vertebrae (C3), is described. Initial cervical spinal radiographs revealed a concave defect in the ventral aspect of the cranial end plate of C3. However, both this finding and ultrasonographic imaging of the area were inconclusive for a fracture. Nuclear scintigraphy revealed that the lesion was metabolically active, prompting computed tomographic imaging that revealed a fracture of C3. Sequential radiographs documented progressive fusion of C2-C3 and no neurological deficits developed over the 5 years after the injury. Cervical vertebral injuries in horses can lead to various clinical signs including ataxia, weakness, and neck stiffness or pain. Diagnosis with cervical radiographs alone can be challenging and, in some cases as the horse in this report, multiple imaging modalities may be required to establish a definitive diagnosis. Horses without neurological signs may recover successfully with conservative medical management, which was performed in this case. 相似文献
2.
Margaret C. McEntee DVM Donald E. Thrall DVM PhD 《Veterinary radiology & ultrasound》2001,42(3):221-225
Twenty two dogs with an infiltrative lipoma had computed tomographic (CT) images acquired to evaluate the extent of local disease. Ten dogs had undergone at least one cytoreductive surgical procedure (range = 1-3; median = 2) prior to imaging. Twenty dogs had measurable disease on CT images; 2 dogs had diffuse disease at a previous surgical site that could not be measured. Tumor volume (n = 20) ranged from 20 to 5,632 cm3 (median = 345 cm3; mean = 996 cm3). None of the dogs had evidence of bone involvement on the CT images; 2 of the 22 dogs had tumors that did not come into direct contact with osseous structures. All dogs with measurable disease had evidence of a fat opacity mass with variable degrees of muscle infiltration. Eleven of 22 dogs were given intravenous contrast medium prior to image acquisition and there was not evidence of enhancement of the infiltrative lipoma in any dog. Based on CT images, tumors were classified as well-defined in 9 dogs, moderately well-defined in 4, not well-defined in 3 and a mix of well-defined and not well-defined in 6 dogs. Tumors tended to be less well-defined in regions where the infiltrative lipoma interdigitated with normal body fat. It appears CT imaging allows adequate discrimination of tumor with the caveat that differentiation of normal fat from infiltrative lipoma can be problematic. 相似文献
3.
Precise localization of the needle tip during CT-guided percutaneous biopsy is considered to be a key element of a successful procedure. To ensure accuracy, the true needle tip must be differentiated from a false or simulated tip which appears when the CT slice encompasses only the shaft of an angled needle. By obtaining images of an aspiration biopsy needle inserted vertically into a phantom and then incrementally tilting the gantry, the authors were able to compare the characteristic features of the true tip to the simulated tip. The true tip was abrupt and distinct and had an adjacent flame-like low density artifact. The simulated tip was indistinct and tapered, yet still produced the adjacent artifact. We concluded that the shape and distinctness of the end portion of the needle itself, rather than the attendant artifact, were the most reliable criteria for accurate needle tip identification. 相似文献
4.
针对制造业加工现场的环境特点,分析了微机控制系统的干扰来源和途径,介绍了实用的抗干扰措施。实践证明:这些软硬件抗干扰措施的综合运用,使自动化加工中微机控制系统的稳定性得到了较大的提高。 相似文献
5.
依据电力系统的近似数学模型,提出了适用于稳定供电电压的无功电压控制曲线。在此基础上,论述了应用插值公式的静止无功补偿计算机控制方法。该方法应用简便,具有较好的动静态特性。 相似文献
6.
7.
本文建立了农业综合生产能力的评价指标体系,讨论了两种评价方法,并通过计算机测评系统,对河南省农业综合生产能力进行了系统的测算和分析。 相似文献
8.
采用TP—801单板机制作作物活体多探头测量仪。该机可在田间对生长状态下的农作物进行多点体内养分积累、运输、分配等测定,且结果可靠。 相似文献
9.
This paper presented a metnod of self-determining PID parameters by using system idenification and gave a engineering sample. 相似文献
10.
本文介绍浦沅工程机械总厂准柔性制造系统(P-FMS)中加工箱体零件所用的一个工艺规程自动设计系统—HUDACAPP,阐述了系统的原理、结构和实现.给出了实例.本系统能按零件输入信息自动生成工艺过程,选择机床、夹具、刀具、量具、切削参数以及计算工时,并能与P-FMS的实时管理调度软件联接,提供所需的资料. 相似文献