全文获取类型
收费全文 | 1330篇 |
免费 | 227篇 |
国内免费 | 151篇 |
出版年
2024年 | 6篇 |
2023年 | 58篇 |
2022年 | 46篇 |
2021年 | 69篇 |
2020年 | 71篇 |
2019年 | 97篇 |
2018年 | 63篇 |
2017年 | 68篇 |
2016年 | 71篇 |
2015年 | 73篇 |
2014年 | 72篇 |
2013年 | 91篇 |
2012年 | 55篇 |
2011年 | 62篇 |
2010年 | 39篇 |
2009年 | 55篇 |
2008年 | 42篇 |
2007年 | 38篇 |
2006年 | 35篇 |
2005年 | 45篇 |
2004年 | 27篇 |
2003年 | 41篇 |
2002年 | 45篇 |
2001年 | 28篇 |
2000年 | 27篇 |
1999年 | 25篇 |
1998年 | 26篇 |
1997年 | 18篇 |
1996年 | 22篇 |
1995年 | 24篇 |
1994年 | 20篇 |
1993年 | 29篇 |
1992年 | 40篇 |
1991年 | 38篇 |
1990年 | 17篇 |
1989年 | 8篇 |
1988年 | 7篇 |
1987年 | 6篇 |
1986年 | 6篇 |
1985年 | 18篇 |
1984年 | 21篇 |
1983年 | 9篇 |
1982年 | 12篇 |
1981年 | 5篇 |
1980年 | 7篇 |
1979年 | 6篇 |
1978年 | 8篇 |
1977年 | 5篇 |
1976年 | 3篇 |
1971年 | 1篇 |
排序方式: 共有1708条查询结果,搜索用时 15 毫秒
1.
目的:研究和比较不同的治疗方式(责任节段治疗与整体治疗)治疗多节段腰椎间盘突出症(Herniation of Mutisegmented Lumber Intervertebral Disc,HMLD)的临床疗效及安全性。方法:对2010.01年至2013.01在我科明确诊断为多节段腰椎间盘突出且行手术治疗的共计78例患者进行回顾性分析。按照治疗方式的不同分为责任节段组(实验组,42例)和整体治疗组(对照组,36例)。结合手术前后的随访资料,评价并比较两组患者的疼痛模拟评分(VAS)、JOA功能评分及围手术期的手术时间、术中出血量、术后下地时间,花费,并发症等指标。结果:实验结果显示,实验组与对照组在术后6月,12月及36月的VAS疼痛评分及JOA评分的比较中并无显著性差异(P0.05)。但术后第二日实验组患者的疼痛程度显著好于对照组(P0.05)。实验组的术中出血量、花费及下地时间显著优于对照组(P0.05)。在并发症方面,术后1年内,实验组的并发症发生率显著优于对照组(P0.05);术后1年后,对照组的发生率较好,但两组间均无统计学差异(P0.05)。结论:对于多节段椎间盘突出症,找到责任节段并针对责任节段进行治疗较整体治疗来讲,能够在取得相似治疗效果和安全性的同时,能够有效的减少花费,手术创伤及术后疼痛指标,并能有效减少短期并发症的发生。在多节段腰椎间盘突出症的治疗中可以作为一种推荐的手术术式。 相似文献
2.
Coactivation is an important component for understanding the physiological cost of muscular and spinal loads and their associations with spinal pathology and potentially myofascial pain. However, due to the complex and dynamic nature of most activities of daily living, it can be difficult to capture a quantifiable measure of coactivation. Many methods exist to assess coactivation, but most are limited to two-muscle systems, isometric/complex analyses, or dynamic/uniplanar analyses. Hence, a void exists in that coactivation has not been documented or assessed as a multiple-muscle system under realistic complex dynamic loading. Overall, no coactivation index has been capable of assessing coactivation during complex dynamic exertions. The aim of this review is to provide an understanding of the factors that may influence coactivation, document the metrics used to assess coactivity, assess the feasibility of those metrics, and define the necessary variables for a coactivation index that can be used for a variety of tasks. It may also be clinically and practically relevant in the understanding of rehabilitation effectiveness, efficiency during task performance, human-task interactions, and possibly the etiology for a multitude of musculoskeletal conditions. 相似文献
3.
The neutralization of acidic coal mine lakes by additions of natural organic matter: a mesocosm test
Cylindrical polyethylene enclosures 3 m in length and 1 m in diameter reaching from the surface to the bottom were constructed in an acid (pH=3.1) lake on a coal surface mine in southern Illinois. Wheat straw was added to the enclosures to test the effects of dissimilatory sulfate reduction on water chemistry. Added straw increased sulfide concentrations, raised pH to 6.5, reduced O2 and increased acid neutralizing capacity of the enclosed water columns when compared with a control enclosure and with the open lake. Generation of acid neutralizing capacity exceeded the standing stock of sulfide indicating that sulfide was removed either by precipitation of FeS or outgassing of H2S. The pH and acid neutralizing capacity within the enclosures eventually returned to the level of the surrounding lake because of water exchange around the enclosure walls. Our results show that additions of organic matter to acid surface mine lakes result in the generation of acid neutralizing capacity. 相似文献
4.
目的:探讨腰椎旁神经阻滞联合超短波对腰椎间盘突出症疼痛及腰背肌生物力学性能的影响。方法:选择我院2014年2月~2016年8月收治的98例腰椎间盘突出症患者,按抽签法分组对照组与研究组。对照组采用腰椎旁神经阻滞治疗,研究组基于对照组加用超短波治疗。观察两组的临床疗效、治疗前后视觉模拟评分(VAS)、60°/s角速、120°/s角速平均功率(AP)、峰力矩(PT)、腰背屈/伸比值(F/E)、血清P物质(SP)、β-内啡肽(β-EP)、白细胞介素-6(IL-6)、肿瘤坏死因子-α(TNF-α)水平的变化及不良反应的发生情况。结果:研究组总有效率为95.91%,显著高于对照组,差异有统计学意义(P0.05)。治疗后,两组F/E值、血清SP、IL-6、TNF-α水平均较治疗前显著降低,且研究组以上指标均明显低于对照组,两组AP、PT、血清β-EP水平均较治疗前明显上升,且研究组以上指标显著高于对照组,差异均有统计学意义(P0.05)。两组不良反应的发生率比较差异无统计学意义(P0.05)。结论:腰椎旁神经阻滞联合超短波治疗腰椎间盘突出症的效果明显优于单用腰椎旁神经阻滞治疗,其可有效缓解疼痛及改善腰背肌生物力学性能,并减轻炎症反应。 相似文献
5.
《Animal : an international journal of animal bioscience》2017,11(2):261-273
There is increasing interest in the use of continuous housing systems for dairy cows, with various reasons put forward to advocate such systems. However, the welfare of dairy cows is typically perceived to be better within pasture-based systems, although such judgements are often not scientifically based. The aim of this review was to interrogate the existing scientific literature to compare the welfare, including health, of dairy cows in continuously housed and pasture-based systems. Although summarising existing work, knowledge gaps and directions for future research are also identified. The scope of the review is broad, examining relevant topics under three main headings; health, behaviour and physiology. Regarding health, cows on pasture-based systems had lower levels of lameness, hoof pathologies, hock lesions, mastitis, uterine disease and mortality compared with cows on continuously housed systems. Pasture access also had benefits for dairy cow behaviour, in terms of grazing, improved lying/resting times and lower levels of aggression. Moreover, when given the choice between pasture and indoor housing, cows showed an overall preference for pasture, particularly at night. However, the review highlighted the need for a deeper understanding of cow preference and behaviour. Potential areas for concern within pasture-based systems included physiological indicators of more severe negative energy balance, and in some situations, the potential for compromised welfare with exposure to unpredictable weather conditions. In summary, the results from this review highlight that there remain considerable animal welfare benefits from incorporating pasture access into dairy production systems. 相似文献
6.
Production of vitamin B12 in an upflow anaerobic filter continuous reactor using Acetobacterium sp. 总被引:2,自引:0,他引:2
Alberto Emilio Bainotti Belén Estebanez Hisashi Nagadomi Naomichi Nishio 《Biotechnology letters》2000,22(6):503-508
The accumulation of biofilm by Acetobacterium sp. during continuous culture in an upflow anaerobic filter (UAF) growing on methanol-formate was the result of space velocity and inlet concentrations of substrate and Co+2. To achieve good development of biofilm, a space velocity of 0.38 h–1, inlet substrate concentrations of 125 mM of both methanol and formate, and Co+2 at 0.16 mM were required. Cell productivities in the effluent of the UAF-reactor were about 6-fold higher than in chemostat cultures (0.20 g l–1 h–1 for UAF and 0.035 g l–1 h–1 for chemostat) (previous studies), and the maximum vitamin B12 specific concentration was 5.1 mg g cell–1. 相似文献
7.
《Journal of molecular biology》2021,433(22):167254
Tau is an intrinsically disordered protein implicated in many neurodegenerative diseases. The repeat domain fragment of tau, tau-K18, is known to undergo a disorder to order transition in the presence of lipid micelles and vesicles, in which helices form in each of the repeat domains. Here, the mechanism of helical structure formation, induced by a phospholipid mimetic, sodium dodecyl sulfate (SDS) at sub-micellar concentrations, has been studied using multiple biophysical probes. A study of the conformational dynamics of the disordered state, using photoinduced electron transfer coupled to fluorescence correlation spectroscopy (PET-FCS) has indicated the presence of an intermediate state, I, in equilibrium with the unfolded state, U. The cooperative binding of the ligand (L), SDS, to I has been shown to induce the formation of a compact, helical intermediate (IL5) within the dead time (∼37 µs) of a continuous flow mixer. Quantitative analysis of the PET-FCS data and the ensemble microsecond kinetic data, suggests that the mechanism of induction of helical structure can be described by a U ↔ I ↔ IL5 ↔ FL5 mechanism, in which the final helical state, FL5, forms from IL5 with a time constant of 50–200 µs. Finally, it has been shown that the helical conformation is an aggregation-competent state that can directly form amyloid fibrils. 相似文献
8.
杀虫剂不同施用方式对烟蚜抗药性发展和羧酸酯酶活力的影响 总被引:1,自引:0,他引:1
室内模拟田间杀虫剂施药方式,研究3种杀虫剂连用及其顺序轮用对烟蚜Myzus persicae(Sulzer)抗药性发展和羧酸酯酶活力的影响。结果表明,氧化乐果、灭多威、高效氟氯氰菊酯连续施药9次后,其抗性分别增长73.3,8.9,10.4倍;氧化乐果→灭多威→高效氟氯氰菊酯顺序轮用3次(施药9次)后,氧化乐果抗性指数增长了47.3倍,灭多威抗性指数增长了6.7倍,高效氟氯氰菊酯抗性指数增长了5.0倍。羧酸酯酶活力检测结果表明,3种杀虫剂连用9次后,烟蚜种群的α-NACarE活力分别增长了20.0,24.0和15.6倍,酶活力在0.6(OD600nm/aphid/min)以上的个体比例分别增加了73.4%,87.6%和43.8%;而3种杀虫剂顺序轮用3次(施药9次)后,烟蚜种群的α-NACarE活力增长了10.2倍,酶活力在0.6以上的个体比例增加了4.8%。结果证实杀虫剂轮换施用能延缓烟蚜抗药性的发展和烟蚜种群α-NACarE活力及高活力个体频率的增加。 相似文献
9.
Ervin Pihu 《Hydrobiologia》1996,340(1-3):163-172
The management of aquatic weeds in an irrigation scheme is constrained by the agro-economic system in relation to scheme layout, the nature and ecology of the aquatic weeds, agricultural practice, irrigation and drainage requirements, and the available resources for maintenance. The way in which the ecology, engineering and economics of irrigation and drainage channels interact to produce a pattern of management is investigated for the Mwea Irrigation Settlement Scheme, Central Province, Kenya. This is used to develop a simple model which enables the economic implications of varying the aquatic weed management practice to be identified. The model brings the selection of a weed control programme within the principles of engineering economy. 相似文献
10.
Lumbar interbody fusion is currently the gold standard in treating patients with disc degeneration or segmental instability. Despite it having been used for several decades, the non-union rate remains high. A failed fusion is frequently attributed to an inadequate mechanical environment after instrumentation. Finite element (FE) models can provide insights into the mechanics of the fusion process. Previous fusion simulations using FE models showed that the geometries and material of the cage can greatly influence the fusion outcome. However, these studies used axisymmetric models which lacked realistic spinal geometries. Therefore, different modeling approaches were evaluated to understand the bone-formation process.Three FE models of the lumbar motion segment (L4–L5) were developed: 2D, Sym-3D and Nonsym-3D. The fusion process based on existing mechano-regulation algorithms using the FE simulations to evaluate the mechanical environment was then integrated into these models. In addition, the influence of different lordotic angles (5, 10 and 15°) was investigated. The volume of newly formed bone, the axial stiffness of the whole segment and bone distribution inside and surrounding the cage were evaluated.In contrast to the Nonsym-3D, the 2D and Sym-3D models predicted excessive bone formation prior to bridging (peak values with 36 and 9% higher than in equilibrium, respectively). The 3D models predicted a more uniform bone distribution compared to the 2D model.The current results demonstrate the crucial role of the realistic 3D geometry of the lumbar motion segment in predicting bone formation after lumbar spinal fusion. 相似文献